Barriers to accessing prescribed medical cannabis: qualitative insights from people using non-prescribed cannabis for medicinal purposes in the Netherlands

Abstract

Background

Although medical cannabis has been legally available by prescription in the Netherlands for more than two decades, few individuals use it. Instead, most people who use cannabis for therapeutic purposes continue to obtain it through unregulated, illicit sources. This study examined barriers to accessing prescribed cannabis from the perspectives of people using non-prescribed cannabis for medicinal purposes in the Netherlands.

Methods

Semi-structured qualitative interviews were conducted with thirty-three participants who used non-prescribed cannabis to manage somatic or psychiatric symptoms. Data collection and analysis were guided by Levesque and colleagues’ patient-centred access to care framework, which encompasses five dimensions of accessibility: affordability, availability, approachability, appropriateness, and acceptability. The framework provides a multidimensional view of access within healthcare systems. A deductive coding approach and thematic analysis were applied. Reporting followed the COREQ guidelines.

Results

Participants reported barriers across all five dimensions of the access to care framework. Key challenges included the perceived high cost of prescribed cannabis, the limited availability of prescribing physicians, restrictive medical guidelines, and a lack of accurate and accessible information. Additional barriers were the perceived poor fit between services and patient needs, particularly in terms of cannabis product variety and effectiveness, as well as persistent stigma surrounding cannabis use. While most participants expressed a preference for prescribed cannabis in principle—valuing its safety, quality, and legitimacy—these perceived barriers prevented or dissuaded them from access through the formal healthcare system.

Conclusions

Despite its longstanding legal status, access to prescribed cannabis in the Netherlands remains constrained by significant structural, informational, and sociocultural barriers. Addressing these barriers requires coordinated policy reforms and healthcare responses to ensure equitable, patient-centred access to prescribed cannabis and reduce reliance on unregulated sources.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12954-025-01369-8.

Background

In the Netherlands, cannabis for recreational use has been widely available in coffeeshops1 since the 1970s [2], while cannabis for medicinal purposes has been legally accessible by prescription through specialized pharmacies since 2003 [3]. Despite having one of the longest-standing medical cannabis programs in the world, the vast majority of people who use cannabis for therapeutic purposes in the Netherlands do so without a prescription [4]. A 2020 survey of a representative sample of Dutch adults found that approximately 95% of individuals using cannabis medicinally obtained it from unregulated sources such as coffeeshops, cannabis social clubs,2 dealers, or home cultivation [4]. Based on these findings, an estimated 460,000 adults use non-prescribed cannabis for medicinal purposes, while only 7,300 patients received prescribed cannabis in 2023 (population 18 million) [5]. The reasons underlying this limited uptake of prescribed cannabis remain poorly understood.

Prescribed cannabis in the Netherlands is regulated by the Office of Medicinal Cannabis, a division of the Dutch Ministry of Health. Five strains of herbal cannabis with varying concentrations of tetrahydrocannabinol (THC) and cannabidiol (CBD) are available. These can be dispensed directly or processed by specialized pharmacies into sublingual oils or topical formulations [3]. Any licensed physician may prescribe cannabis, including general practitioners and specialists, with general practitioners accounting for approximately 65% of all prescriptions [6]. Cannabis may be considered when standard treatment options and medications are insufficiently effective or cause too many side effects [3]. There is no predefined list of eligible medical conditions, allowing physicians considerable flexibility in deciding when to prescribe cannabis [3]. Although no centralized registry of prescribed cannabis patients exists, recent research indicates that chronic pain is the most common reason for prescribing in the Netherlands [7]. In 2023, the price of prescribed herbal cannabis was €6.50 per gram [8], compared with average prices in coffeeshops, which range from €13 per gram for the most popular herbal cannabis to €4 per gram for imported herbal cannabis [9]. Prescribed cannabis oil ranges from €50 to €150 per 10 ml [10]. Products can be shipped to local pharmacies, eliminating the need for patients to visit one of the three specialized pharmacies in person. Despite this seemingly flexible and permissive regulatory framework, barriers to access persist.

A key turning point occurred in 2018, when the Dutch College of General Practitioners (Nederlands Huisartsen Genootschap, NHG) issued a position paper advising against prescribing cannabis except in palliative care, citing insufficient scientific evidence of efficacy [11]. Following the release of this recommendation, health insurers stopped reimbursement for prescribed cannabis [12]. The number of cannabis prescriptions declined steadily from over 53,000 in 2017 to fewer than 39,000 in 2023 [5, 13]. This marked a sharp trend reversal from the previous decade, when prescriptions had increased from fewer than 5,000 in 2007 to more than 50,000 in 2017 [14]. It is important to note that the position paper of the Dutch College of General Practitioners was based on a limited review of the literature, which included only blinded randomized controlled trials (RCTs) conducted before 2016 for five conditions (e.g. chronic pain, epilepsy) [15]. Critics argue that RCTs are not well-suited to evaluating medical cannabis, as these trials require standardized and stable products, while plant-based cannabis preparations are difficult to standardize and contain multiple active compounds that interact [16, 17]. In addition, robust RCT evidence remains scarce due to technical, economic, regulatory, and legal constraints on medical cannabis research [18–20]. In this context, real-world observational studies and patient-reported outcomes provide valuable information on the therapeutic benefits of cannabis [16, 17].

From a public health perspective, self-medication with unregulated cannabis raises significant concerns. Unregulated products may contain potentially harmful contaminants—including microbes, heavy metals, and pesticides—which present potential health risks to the consumer [21–24]. Moreover, individuals using these products do so without medical supervision, dosing guidance, or monitoring of side effects and drug interactions. This is particularly concerning for people with chronic health conditions, who may be at greater risk of experiencing adverse outcomes. Physicians can play a crucial role in supporting these patients by providing tailored guidance, monitoring treatment outcomes, and mitigating potential harms [3]. However, few physicians in the Netherlands are currently trained to provide such guidance, as medical cannabis is not part of standard medical education. Ensuring access to regulated cannabis under proper medical supervision is imperative to safeguard patient health and well-being.

The present study examines barriers to accessing prescribed medical cannabis from the perspectives of people who use non-prescribed cannabis for medicinal purposes. By centring the experiences of this population, the study aims to generate insights that can help inform clinical practice and policy responses to reduce barriers to care.

Methods

Study design

This qualitative study collected data through semi-structured interviews with individuals who self-reported current use of non-prescribed cannabis for medicinal purposes. Medicinal use was defined as the use of cannabis-based products to manage somatic or psychiatric symptoms. The study received an exemption from ethics review from the Medical-Ethical Review Committee METC NedMec (22-912/DB) and was evaluated and approved by the Trimbos Institute Ethical Review Committee (registration number 202213). Reporting followed the Consolidated Criteria for Reporting Qualitative Research (COREQ) guidelines (Supplementary Material S1) [25].

The study adopted a largely deterministic analytical approach to identify consistent and replicable themes related to barriers to care, while also incorporating reflexive elements during the interviews and analysis to enhance contextual depth and interpretation [26]. This approach aligned with the study’s objective to identify key barriers to prescribed cannabis in order to inform strategies for improving patient-centred access to care.

Data collection

Between February and April 2023, thirty-three individual interviews were conducted by three interviewers using a semi-structured interview guide. Four individuals did not attend their scheduled interview without explanation, and one cancelled due to illness; attempts to reschedule were unsuccessful. Interviews lasted between 25 and 70 min (average 45 min) and were conducted online via Microsoft Teams at times convenient for participants. Thirty-one interviews were held in Dutch and two in English. One participant disclosed a brain injury during the interview. Out of respect for the participant, the interviewer chose to complete the interview. However, due to inconsistencies in responses, the transcript was excluded from analysis beyond the demographic characteristics. None of the remaining participants appeared intoxicated; all responded to questions coherently and attentively. Participants provided written and oral informed consent and received a €40 online shopping voucher as compensation. Data collection and storage complied with the European Union General Data Protection Regulation. Personal identifiers were removed during transcription to ensure anonymity, and data was stored securely on password-protected systems.

Participant recruitment

In line with qualitative research recommendations [27], we aimed to recruit approximately thirty participants to capture a range of experiences related to the medicinal use of cannabis. Participants were recruited through a combination of convenience and purposeful sampling. A large convenience sample (N = 1059) was initially obtained through an online survey study exploring the characteristics of people using non-prescribed cannabis for medicinal purposes [28]. The survey was primarily distributed via Facebook advertisements and to a lesser extent through other online and offline channels. At the end of the questionnaire, respondents could opt to be contacted for follow-up studies. From those who expressed interest, participants were purposefully selected based on predefined criteria. First, we identified individuals who provided rich, detailed responses to open-ended survey questions, as this indicates a higher likelihood of meaningful engagement in an interview setting. Then we sought diversity in age, gender, and health conditions to ensure variation in perspectives. Selected individuals were contacted via email and provided with detailed information about the study and a consent form. Interviews were conducted until the research team agreed that data saturation was reached.

Eligibility criteria

Eligibility criteria included being aged 18 or older, currently residing in the Netherlands, fluent in Dutch or English, having Internet access for online interviewing, and self-reported current use of non-prescribed cannabis-based products for physical or mental health symptoms. Individuals who used both prescribed and non-prescribed cannabis for medicinal purposes were also eligible. However, those who exclusively used prescribed cannabis or commercially available (non-prescribed) CBD products were excluded.3

Conceptual framework

The study was guided by the patient-centred access to healthcare framework developed by Levesque and colleagues [29]. This multidimensional conceptual framework has been widely used to identify and evaluate barriers to care across diverse healthcare settings [30, 31]. It defines access as the interface between the healthcare system and its potential users. Rather than viewing access solely as being depended on the characteristics of a service, the model is patient-centred, putting the process of seeking, obtaining, and benefitting from care central to the analysis. The framework proposes five dimensions of accessibility: approachability, acceptability, availability, affordability, and appropriateness. Access is limited when individuals cannot identify that services exist or can be reached (approachability), when services are not sufficiently physically available (availability) or financially feasible (affordability), when cultural or social factors reduce willingness to seek care, for example because services are not deemed appropriate to community values (acceptability), or when services do not align with patient needs or expectations (appropriateness).

This framework informed the development of interview questions, guided the analysis of coded data, and facilitated the categorization of emerging themes across its five dimensions. Initially, the research team engaged in a detailed review of the conceptual framework to develop a clear and shared understanding of how each dimension was defined and operationalized by Levesque and colleagues. This step was crucial so that key elements of access to care could be accurately identified within the data. Once this conceptual understanding was established, the framework provided a structured approach for interpreting the data and enabling the mapping of codes and subthemes to the appropriate dimensions. By grounding the analysis in the framework’s definition of each dimension, we ensured that the categorization of emerging themes reflected a coherent, theory-informed understanding of the factors influencing access to prescribed cannabis.

Interview guide

The interview guide was developed by the research team in collaboration with a lived-experience partner who had personal experience using cannabis for medicinal purposes. Interview questions were designed to address each of the five dimensions of the access to care framework. To ensure clarity and relevance, the guide was pilot tested with three individuals, after which minor revisions were made to improve the phrasing and layout of the interview questions. In addition to exploring barriers to prescribed cannabis, the interviews also examined broader contextual factors and participants’ experiences with using non-prescribed cannabis for medicinal purposes, to better understand their motivations and decision-making processes. Questions focused on participants’ experiences, knowledge, and perceptions, and explored how various social, economic, and health-related factors shaped their actions and decisions. Care was taken to avoid leading questions. Examples of interview questions included: ‘Can you tell me how you obtain your cannabis and why you obtain it this way?’ and ‘Have you ever talked about your medicinal use of cannabis with a doctor? If yes, how did that conversation go? If no, why not?’ An English translation of the Dutch interview guide is available in Supplementary Material S2.

Coding

Interviews were video recorded and transcribed verbatim. To protect confidentiality, pseudonyms were assigned, and identifiers were removed. Interviewers (NG, LS, and a research assistant) took notes during and after the sessions. Three researchers (LS and the two coders NG and TM) read all transcripts multiple times to familiarize themselves with the data. A deductive coding approach was used. A codebook was developed based on the interview guide and key topics that emerged during data collection. It included 27 codes across 10 broad thematic categories such as health and wellbeing, consumer behaviour, information, healthcare, prescribed cannabis, cost, and norms and values (see Supplementary Material S3). To ensure coding reliability, two researchers (NG and TM) independently coded all meaningful text segments in MAXQDA 2022 to create a useful division of the data [32]. After coding three initial transcripts, discrepancies were reviewed and discussed to refine the codebook. Interrater agreement on the first 20% of interviews (n = 6) was 92%, exceeding the minimum required threshold of 80% [33]. Once all transcripts were coded, codes were compared and any disagreements were discussed until consensus was reached.

Thematic analysis

A traditional approach to thematic analysis was used, with coding reliability and the development of topic-summary-type themes [26, 34, 35]. A theme was defined as capturing “something important about the data in relation to the research question and [representing] some level of patterned response or meaning within the data set” [36]. Thematic analysis of coded data was guided by the research question and structured around the five dimensions of the patient-centred access to care framework. It was carried out by three researchers (NG, TM, LS) to ensure consistent interpretation of the data. Themes were identified within the coded data and developed through an iterative process. Reflective sessions were held throughout the analytical process to critically review interpretations [34]. Once a preliminary set of themes was developed, they were refined in discussion with the lived-experience partner, who helped reframe themes for accuracy and tone by replacing clinical language with patient-centred wording. He also added nuance by incorporating contextual and emotional dimensions that had initially been overlooked.

Research team

The research team consisted of four scientific researchers with expertise in drug use and dependence and academic backgrounds in psychology, criminology, anthropology, and public health. Three held a PhD and one held a Master’s degree. The team included three women and one man. All had prior training and experience conducting qualitative research with people who use drugs. In preparation for the current study, interviewers received additional training in interview techniques. The last author, an expert in qualitative research methods and healthcare research, provided methodological guidance throughout the study and reviewed the analytical process to enhance external validity of the findings. Minimal relationships were established with participants prior to beginning the interviews. The interviewers introduced themselves and outlined their professional role, the focus of their daily work, and their motivation for engaging with the research topic.

Recognizing the value of patient involvement in producing meaningful research, a lived-experience partner—an individual with lived experience using cannabis for medicinal purposes—was actively involved throughout the research process. He contributed to the development of the interview guide, the refinement of themes, and the interpretation of findings, ensuring that patient perspectives remained central to the study.

Results

Analysis of the interview data revealed several key themes related to the accessibility of prescribed medical cannabis, organized according the five dimensions of the patient-centred access to care framework: affordability, availability, approachability, appropriateness, and acceptability. We first provide a brief overview of participant characteristics, followed by a detailed presentation of the major themes. Themes are presented in no particular order and are illustrated with participant quotations to demonstrate that findings are grounded in the data. Divergent perspectives were considered in the analysis and are described throughout the findings to capture the diversity of participant experiences.

Participant characteristics

Thirty-three individuals who used non-prescribed cannabis for medicinal purposes participated in the interviews (Table 1). The majority was male (60.6%, n = 20), with a mean age of 45 years (range 22 to 71). More than half (57.6%, n = 19) reported being unfit for work or disabled, while 33.4% (n = 11) were employed full- or part-time. Most participants had completed upper secondary or vocational secondary education (36.4%, n = 12). The majority was Dutch (90.9%, n = 30), with three international participants. Most participants (84.8%, n = 28) exclusively used non-prescribed cannabis for medicinal purposes, while a smaller group (15.2%, n = 5) reported using both prescribed and non-prescribed products. Coffeeshops were the primary source of cannabis for most participants (57.6%, n = 19) and herbal cannabis was the most commonly used form (66.7%, n = 22). Participants reported a wide range of physical and mental health conditions, with the most common being chronic pain and sleep disorders. The majority (87.9%, n = 29) reported more than one condition (Table 2).

Table 1.

Participant characteristics (N = 33)

Variables	%	n
Gender
Male	60.6	20
Female	39.4	13
Age
18–29	12.1	4
30–39	21.2	7
40–49	30.3	10
50–64	30.3	10
65 +	6.1	2
Employment
Unfit for work/disabled	57.6	19
Fulltime	18.2	6
Parttime	15.2	5
Retired	6.1	2
Student	3.0	1
Education
Primary education	3.0	1
Lower/pre-vocational secondary education	27.3	9
Upper/vocational secondary education	36.4	12
Bachelor’s (or equivalent)	27.3	9
Master’s or Doctorate	6.1	2
Nationality
Dutch	90.9	30
Not Dutch	9.1	3
Cannabis type
Non-prescribed cannabis	84.8	28
Non-prescribed and prescribed cannabis	15.2	5
Main source of cannabis
Coffeeshop	57.6	19
Home cultivation	21.2	7
Online shops	9.1	3
Other	12.0	4
Main form of cannabis
Herbal cannabis	66.7	22
Resin cannabis	3.0	1
Sublingual oil	24.2	8
Other	6.1	2

Dutch equivalents of education levels, from lowest to highest: Basisonderwijs; VMBO, MBO1, praktijkonderwijs, onderbouw HAVO/VWO; HAVO, VWO, MBO; HBO, WO Bachelor; WO Master, Doctoraat

Table 2.

Self-reported medical conditions of participants

Health conditions	%	n
Chronic pain	63.6	21
Sleep disorder	42.4	14
Attention-deficit/hyperactivity disorder	39.4	13
Depression	36.4	12
Post-traumatic stress disorder	33.3	11
Anxiety	18.2	6
Fibromyalgia	15.2	5
Autism spectrum disorder	15.2	5
Migraine	12.1	4
Rheumatic diseases	9.1	3
Ehlers Danlos syndrome	6.1	2
Multiple sclerosis	3.0	1
Crohn’s disease	3.0	1
Glaucoma	3.0	1
Other	24.2	8

Participants could select multiple medical conditions from a structured list

Theme 1: Perceived high cost (Affordability)

Affordability emerged as a key factor shaping participants’ choices regarding medicinal cannabis use. Many participants believed that prescribed cannabis was more expensive than cannabis from other sources, such as coffeeshops or home cultivation, citing cost as the main reason for not pursuing a prescription. However, not all participants were aware of the actual price of prescribed cannabis, often basing their assumptions on anecdotal reports rather than firsthand knowledge.

Most participants indicated that they would use prescribed cannabis if it were reimbursed by health insurance. Some had attempted to obtain reimbursement but were denied, while others never even tried to obtain a prescription, because they assumed that the cost would not be covered and that it would be unaffordable out-of-pocket. A few participants had previously received insurance reimbursement for prescribed cannabis, but, when it was terminated in 2018, they could no longer afford it and felt forced to resort to unregulated sources.

Many participants had limited income or relied on disability or welfare benefits due to chronic health conditions that restricted their ability to work. These participants reported being unable to afford prescribed cannabis and/or struggling with the cost of non-prescribed cannabis. Regardless of income, most considered the cost of cannabis a substantial financial burden.

If I have really severe pain, then I really have to use cannabis, because otherwise it is not doable for me. I just can’t. At one point I talked to the general practitioner about it, and yes, it was possible [to get prescribed cannabis, red.], but the cost was so high that it is not affordable if you are on welfare. And yes… then I decided to just grow it myself. (Male, 44) (Translation)

Financial limitations influenced not only whether participants accessed prescribed cannabis, but also their choices regarding non-prescribed cannabis, including what products they used, how much they consumed, and where they obtained it. Some opted for cheaper alternatives, such as home cultivation or purchasing cannabis from dealers instead of coffeeshops. Others used less cannabis than needed or chose less effective but more affordable products. For example, some participants reported that sublingual oil provided better symptom relief than inhaled herbal cannabis, but its higher cost made it inaccessible. Several individuals described how they regularly felt forced to choose between purchasing cannabis for symptom relief and meeting basic needs, such as groceries or leisure activities.

Interviewer (I): Do you also have financial worries because of your medicinal cannabis use?

Participant (P): Yes, sometimes I do and I feel very guilty about that. Then I’m like ‘I'm in pain. I'm really in pain. And I can't go to the doctor.’ You just want to get rid of some of the pain if possible or just be less in pain.

I: You just said you feel a bit guilty. Why is that?

P: Well, you have to forgo other things. You have to cut back on your groceries again, and on other things. (Female, 64) (Translation)

Participants noted that having to compromise on medicinal cannabis use negatively impacted their wellbeing. Reducing the dosage or switching to less effective cannabis products typically resulted in inadequate symptom management. Their inability to afford cannabis on a regular basis also contributed to ongoing stress for participants, further exacerbating their health challenges.

I: Do you ever worry about the costs of cannabis?

P: Every week. Stress, like, ‘how am I going to do that next week? Am I going to beg someone for money again, or ask my mother?’ And yes… That's not so nice… It would just be nice if it was just reimbursed. (Male, 36) (Translation)

Overall, affordability played a critical role in shaping access to and use of medicinal cannabis, with serious implications for participants’ health and quality of life.

Theme 2: Limited availability of prescribing physicians and restrictive medical guidelines (Availability)

Participants generally felt that there were not enough physicians in the Netherlands who prescribe cannabis. While a few reported positive experiences with physicians who were open to prescribing it, most had had negative encounters or assumed that their physician would reject their request for prescribed cannabis.

Participants reported that physicians seemed to have limited knowledge about prescribed cannabis, including its medicinal properties, available products, eligibility criteria, and prescription procedure. They also noted that physicians with less knowledge of cannabis were less open to prescribing it. Some participants described interactions where physicians expressed prejudices or negative attitudes towards cannabis.

A lot of general practitioners still have really limited knowledge of it. You have to be a bit lucky with who you get in front of you. And there is not some kind of standard protocol where it is easier to say 'Gosh, just give it a try.' (Male, 35) (Translation)

I: Did you feel comfortable discussing it with your general practitioner?

P: No. [Because of] the stigma I mentioned earlier. And also because I know that many general practitioners have limited knowledge about it. From what I understand, it is not part of the standard curriculum for general practitioners. So yeah, I also noticed that in this conversation, that there was just relatively little prior knowledge. And that also caused a certain tension for the general practitioner: ‘Oh, oh, oh, yes, well, oh, yes, it is good that you are looking for a way to deal with the pain, buuut…’ [laughs] […] I also read that there was actually a call for general practitioners to learn more about this. Because there is a lack of knowledge. (Male, 35) (Translation)

Several participants shared frustrating experiences in which physicians cited medical guidelines or recommendations as reasons for not prescribing cannabis. The recommendation from the Dutch Society of General Practitioners (NHG), which advises against prescribing cannabis outside of palliative care, was explicitly mentioned. Participants noted that physicians often viewed cannabis as a treatment of last resort rather than a viable treatment option. A few participants reported that their physicians were in principle willing to prescribed cannabis but felt constrained by guidelines and recommendations.

If it was just easier… Hmm I don’t want to say ‘easy to get’… If you didn’t have to go through all these hoops, like it was the last resort. Because that’s really off-putting. I also don’t want to try all these other drugs that I don’t really know 100%, only to then end up with cannabis that I know. It feels like a bit of a test… like a bit of a performance. I just wish cannabis was seen the same as other drugs. And that it was also a first option if they felt it would work. (Male, 28, expat)

Some participants said they did not even attempt to request a prescription because they expected their request to be rejected. This was driven not only by doubts about meeting eligibility criteria, but also by fear of being judged by their physicians. These expectations were sometimes rooted in previous negative experiences in the healthcare system, where they felt their concerns had been dismissed or met with prejudice. Participants said they chose to not ask for a prescription in order to avoid disappointment or uncomfortable or distressing interactions with their physicians.

I think I would not feel heard [by a doctor]. And that makes me uncomfortable to ask for [a prescription]. If you know that it is very likely that you will get a ‘No’, then you don’t really want to try. (Male, 35) (Translation)

Also the process of obtaining prescribed cannabis was perceived by some participants as inconvenient. Both the initial request for a prescription and the process of obtaining repeat prescriptions were described as bureaucratic and time-consuming. Additional concerns included the lack of specialized pharmacies in their vicinity and long delivery times. Interestingly, these perceptions were mostly based on assumptions or experiences with other medications rather than direct experiences with prescribed cannabis. Participants who had obtained cannabis prescriptions generally reported a smooth prescription process and quick postal delivery.

I just find prescriptions a hassle – requesting a repeat prescription, and it all takes time, and then you have to hope that nothing went wrong again, and eh… I have experienced that too. So I prefer to have it in my own hands. (Female, 30) (Translation)

Some participants expressed that coffeeshops were simply more convenient, because they are widely available, with long opening hours, and low-threshold access.

As long as it's all freely available, I don’t think that I would switch to that [prescribed cannabis, red.]. Unless, let's say, the state accepts all that and there's a lot more choice and there's not such a stigma attached to it. But right now, it's all so cumbersome that I don't bother with it. (Female, 49) (Translation)

Taken together, participants viewed the limited number of prescribing physicians, restrictive medical guidelines, and the perceived inconvenience of obtaining a prescription as major barriers to accessing prescribed cannabis.

Theme 3: Lack of accurate and accessible information (Approachability)

The lack of accurate information shaped participants’ perceptions of how accessible prescribed cannabis was. Although participants were generally aware that prescribed cannabis existed in the Netherlands, many found it challenging to obtain clear information about it.

Most participants relied on the Internet as their primary source of information about prescribed cannabis, some consulted their physicians, and others had not actively sought information about prescribed cannabis. Those who searched online often described official resources, such as government websites, as difficult to navigate. Even when they did find information on such websites, they felt it was insufficient for their needs. For instance, participants noted a lack of clarity around eligibility criteria and insufficient guidance on product types or dosing recommendations.

Rather than focusing exclusively on prescribed cannabis, participants typically searched for information about the medicinal use of cannabis more broadly. Many turned to informal (non-governmental, non-medical) sources, such as websites of cannabis social clubs, medicinal cannabis user groups (set up by patients for patients), Facebook groups, online forums (e.g., Reddit), and patient associations. These platforms were described as important hubs for sharing experiences and exchanging advice, where individuals sought to support one another due to the lack of guidance from official authorities.

P: I'm a lot in those Facebook groups of people with fibromyalgia or rheumatism… So I also read from other people, and you just see that everyone is searching. A lot of people are… They just have no idea what to do. So, yeah, it really has a big impact on your life [when you are sick and don’t receive adequate help to manage your symptoms, red.].

I: And what do you think about the fact that all those Facebook groups exist?

P: It does help me. I think it's good. For lack of better options or support. And you're a bit lonely with all those symptoms. (Female, 63) (Translation)

These informal websites were also used as indirect sources of information about prescribed cannabis. During the interviews, participants frequently referred to what they had ‘heard or read from other people’ online. For instance, most participants believed they were not eligible for a prescription because they had seen lists of only a few qualifying conditions on informal websites. As a result, many participants were discouraged from seeking further information or consulting a physician. In reality, no official list of eligible conditions exists in the Netherlands. Some participants also mentioned reading online about potential drawbacks of prescribed cannabis, such as concerns over irradiation and perceptions of lower quality of prescribed cannabis compared with non-prescribed cannabis.

I once looked it up [on the internet]. I also once talked about it with my general practitioner at the time. But anyway, it’s not reimbursed for the reasons that I use it [cannabis]. But I heard from people who get their cannabis from the pharmacy that the price is higher and the quality is lower. So, yeah, then the choice is made very quickly. […] Eh… yeah, I don’t really know that much about it. What I just said is what I heard from others. So I can’t really say with any certainty how reliable that information is. But I just hear that the quality is, on average, a lot lower than what you get in the coffeeshop. (Female, 50) (Translation)

Overall, the availability and quality of information—including widespread misinformation—strongly influenced participants’ views of prescribed cannabis, shaping their willingness and motivation to pursue it.

Theme 4: Poor fit between services and patient needs (Appropriateness)

In Levesque and colleagues’ patient-centred access to care model, appropriateness refers to the alignment between services and patient needs. This includes both the type of services offered and the manner in which they are provided. Participants in our study voiced concerns about both the suitability of available cannabis products and the anticipated interpersonal quality of care.

Participants’ views of prescribed cannabis products were mixed. They generally valued prescribed cannabis for its consistency (i.e. stable THC content), regulated quality, controlled production, and absence of contaminants. However, many doubted its effectiveness in providing adequate symptom relief and raised serious concerns about the quality and variety of available products. In particular, they criticized the limited choice of just five strains and lack of high-THC options. Participants emphasized that a single strain is not equally effective across different individuals and conditions. Some also worried that irradiation might reduce the medicinal properties and negatively affect the aroma. Discussions largely centred on the five herbal cannabis strains; some participants appeared to be unaware that sublingual oils or topical products could be prescribed. One participant noted that she preferred sublingual oils, but believed they were not available via the formal healthcare system and, thus, had not sought a prescription.

I do find that there are only few strains of prescribed cannabis. There are only 4 or 5 strains that are cultivated, so you don't really have that many options. That’s a shame. I think they should start cultivating more strains for prescription cannabis. […] With outdoor cannabis I could at least grow a few more strains and I could just experiment more with what I like and don't like. (Female, 52) (Translation)

Participants also raised concerns about the anticipated interpersonal quality of care. They worried that physicians would not engage them adequately in shared decision-making about their treatment. Although participants valued professional support and guidance, many emphasized the importance of also having their own knowledge and experience with cannabis considered in treatment decisions. Some participants feared that physicians would limit their autonomy and prescribe products or dosages that are not aligned with their needs or preferences, potentially resulting in insufficient symptom relief and a reduced quality of life.

Why make it so difficult?! I know what I want. I know what I benefit from. Help me, damn it! [I feel that I’m] not being taken seriously or that they don’t think along with me. I mean, when you have all that knowledge yourself [as a patient] and you have a discussion with your doctor, then you just want to be taken seriously. It is probably because there is so little knowledge about it, that [doctors] push it away and don’t want to cooperate. (Female, 52) (Translation)

I was disappointed by the [physician’s] reaction, even though I had expected it. When you get a [stigmatizing] reaction like that, then um... Yeah, I don't know if I... Maybe it sounds a bit extreme, but [I] almost don't feel like a full-fledged citizen. Like I’m not taken seriously regarding what I need, with my right to self-determination. Trust in the patient's insight was completely missing, and I thought that was really a shame. [It feels like it’s] not open for discussion, even though I know that it works. That makes the whole situation so difficult. (Male, 35) (Translation)

Although most participants expressed, in principle, a preference for prescribed cannabis due to its regulated quality, their actual motivation to engage with the healthcare system varied considerably. Some indicated a willingness to use prescribed cannabis in its current form, while others said they would only consider a prescription if the products matched their specific needs. A small group expressed no interest in prescribed cannabis at all. These participants typically reported a lack of trust in the government and the state-controlled medical cannabis producer. They described feeling abandoned by the government, particularly when comparing the Dutch context to recent developments in other countries, where medical cannabis appears more easily accessible and even recreational use has been legalized. This sense of being left behind shaped participants’ perception of prescribed cannabis in the Netherlands and reinforced their preference to ‘keep matters in their own hands’ and continue to use non-prescribed cannabis.

The findings reveal a perceived misalignment between the services offered and patients’ needs and expectations. Participants expressed concerns about the effectiveness of prescribed products, the limited variety of strains, and broader distrust of prescribed cannabis, all of which influenced their engagement with the healthcare system.

Theme 5: Stigma (Acceptability)

Interview data indicated that the acceptability of prescribed cannabis as a therapeutic option was shaped by sociocultural factors, with stigma emerging as a key barrier to access. Participants described that stigma was driven by negative associations with cannabis as a recreational drug and a potential substance of abuse.

Participants reported both experienced and perceived stigma from physicians, friends, family, and society at large. Many described being labelled as ‘drug users’ or believing that others saw them this way. Some recalled encounters in which physicians or social contacts were dismissive or judgmental of their medicinal cannabis use, because they believed it was motivated by a desire to get high rather than a therapeutic need.

[My physician] asked me ‘What kind of medication have you been using up until now?’ I said ‘cannabis,’ and she reacted so poorly to it. Really, she just looked at me like I was a junkie. And because I had such a negative experience with sharing honestly that I use cannabis, it taught me very quickly that I have to keep my mouth shut about it if I want them to take me seriously, to hear me tell my story, and not to see me through outdated, prejudiced lenses. (Female, 27) (Translation)

Several participants described how experienced and perceived stigma contributed to internalized stigma. This manifested as shame or feeling that their medicinal cannabis use was inherently wrong or ‘forbidden’.

I always feel a bit like a burden when I use it. I don’t want to bother anyone. And yet I feel like I’m bothering people, while I think that it’s actually something that helps me a lot. But with other people it’s immediately: ‘Oh, no, no, no, no cannabis.’ They see it as a hard drug. So the stigma definitely needs to go down. (Male, 30) (Translation)

Stigma was also experienced in interactions with coffeeshops. As coffeeshops are part of the illicit (albeit tolerated) market, participants reported feeling uncomfortable and judged when purchasing cannabis there. They did not want to obtain cannabis at locations where they might be mistaken for recreational users, because they felt that it conflicted with their identity as patients seeking therapeutic relief.

It's not nice at the coffeeshop here in this city. There's only one for so many residents. It opens at 6 p.m. and there's always a line in front of the door. And then you stand outside in line and you feel watched and stigmatized. You don't have that at a pharmacy. You have much more privacy there. (Male, 41) (Translation)

Stigma also shaped participants’ perceptions of the appropriateness of seeking prescribed cannabis. On one hand, they believed that obtaining a prescription could reduce stigma, by legitimizing cannabis as a medicine and validating their status as patients rather than recreational users. On the other hand, they stated that they did not feel comfortable pursuing a prescription due to fear of being judged or labelled as ‘junkies’ by their physicians.

It's quite a step to talk about it with my general practitioner, because I've never talked to him about it. I'm a bit afraid that I'll be stigmatized, that he'll look at me differently from then on. […] That you'll be dismissed as, eh… a weed user, a junkie. Many people still see it as a drug. (Male, 41) (Translation)

Others hesitated because they did not want prescribed cannabis to be documented in their medical record, fearing that this could lead to discrimination or impact access to other necessary medical care.

I: Is that door [to ask for prescribed cannabis, red.] closed for you now?

P: Yes, it is closed. Because the problem is that my request to use cannabis would then be in my medical record. And since I also need psychiatric help and have been on the waiting list for psychiatric help for years, I want to have as few barriers as possible. I want to create as few biases as possible, like: ‘Oh, I see in the file that you want to use cannabis. You must be another junkie’. Because one psychiatrist literally said to me: ‘The only reason why you want to use dexamphetamine is because you are a junkie, and you are manipulating me to get what you need.’ Yeah, duh, I have ADHD and I can’t function without medication. (Female, 27) (Translation)

The legal status of prescribed cannabis was a further factor shaping its acceptability. Many participants wanted a prescription to avoid the stress and discomfort associated with obtaining cannabis from unregulated sources. They did not want to contribute to criminal activities by purchasing from illicit suppliers and feared legal repercussions such as eviction if police were to discover their home cultivation. Participants also noted that the illegal status of non-prescribed cannabis reinforced societal stigma towards cannabis, which extended to prescribed cannabis.

Despite these challenges, participants emphasized the importance of autonomy and their right to self-determination in accessing a treatment that is effective for them. They argued that patients should be able to choose cannabis as a therapeutic options without facing legal or institutional barriers.

I just want to be able to get my medicine, just like anyone else. Even if it is, well, let's call it a homeopathic prescription. But then preferably regulated. That is the most important thing for me. (Male, 44) (Translation)

Taken together, stigma significantly influenced the acceptability of prescribed cannabis and shaped patients’ decisions and behaviour regarding its use.

Discussion

This study explored barriers to accessing prescribed cannabis from the perspectives of individuals who self-medicate with non-prescribed cannabis in the Netherlands. Participants reported barriers across all five dimensions of accessibility outlined in Levesque and colleagues’ patient-centred access to care framework [29]. These included the perceived high cost of prescribed cannabis (Affordability), the limited availability of prescribing physicians and restrictive medical guidelines (Availability), the lack of accurate and accessible information (Approachability), concerns about whether services adequately meet patient needs, particularly in terms of cannabis product variety and effectiveness (Appropriateness), and the persistent stigma surrounding cannabis use (Acceptability). The findings provide a multidimensional, patient-centred view on barriers to prescribed cannabis. By grounding the analysis in the patient perspective, this study offers deeper insight into how these obstacles are encountered in practice, extending beyond what is implied by legal frameworks and policies.

Affordability

Affordability emerged as a key barrier to accessing prescribed cannabis in the Netherlands, echoing findings from other countries—such as Germany, Belgium, the United Kingdom, Australia, and North America [37–43] —where high costs, lack of health insurance coverage, and limited financial resources were also reported as significant obstacles. Participants emphasized that the out-of-pocket costs made prescribed cannabis inaccessible, particularly for those with low income or receiving welfare or disability benefits. Expanding insurance coverage could therefore play a critical role in improve equity in access. The Netherlands could draw on policy models from Germany and the Czech Republic, where insurance covers reimbursement of prescribed cannabis for specific medical conditions [44, 45]. In addition, emerging cost-effectiveness analyses may help guide policymakers and encourage insurers to broaden reimbursement [46–48].

Physicians and medical guidelines

A consistent theme across interviews was the difficulty participants faced in finding a physician willing to prescribe cannabis. Participants said that physicians appeared insufficiently informed, sceptical, or dismissive of prescribed cannabis, which either prevented them from obtaining a prescription or discouraged them from seeking one. These experiences align with studies from other countries showing that physicians often feel inadequately informed about medical cannabis and worry about its potential for misuse [39–41, 43, 49–52]. Finding a prescribing physician thus appears to depend more on luck than on a well-structured healthcare system. Variations in physicians’ knowledge and attitudes risk creating inequities in patient care and health outcomes, underscoring the need for targeted education and training to improve knowledge and reduce stigma surround medical cannabis.

Medical guidelines and the position paper of the Dutch College of General Practitioners emerged as systemic barriers to accessing prescribed cannabis. Participants reported that physicians often viewed cannabis as a treatment of last resort rather than a viable therapeutic option, citing medical guidelines as justification. In reality, however, the Netherlands does not have formal medical guidelines for prescribing medical cannabis. Instead, there is merely an informational brochure for physicians stating that cannabis may be considered when standard treatment options are not effective enough or cause too many side effect [3]. The brochure does not specify that all conventional therapies must first be exhausted; yet, many physicians adopt this conservative interpretation.

Participants also noted that some physicians felt constrained by the position paper of the Dutch College of General Practitioners (NHG), which advises that cannabis should not be prescribed except for in palliative care. As outlined in the introduction, this position paper is based on a narrow interpretation of the evidence, drawing only on RCTs while overlooking real-world observational data, which may be better suited for evaluating plant-based medicines. Developing clear, evidence-informed medical guidelines—which acknowledge different kinds of evidence—could provide physicians with greater clarity and confidence. Care should be taken to avoid issuing separate recommendations, such as the NHG position paper, as this risks creating conflicting guidance and inconsistent prescribing practices.

It is also important to note that, unlike in other countries, people in the Netherlands are unlikely to seek medical cannabis for non-medical purposes or for conditions other than the ones they report to their physician. As noted above, patients often must first try all conventional treatment options for a given condition before being allowed to try prescribed cannabis. Moreover, recreational cannabis is readily accessible through licensed coffeeshops. The many barriers to accessing prescribed cannabis—such as the lack of reimbursement and reports that Dutch medical cannabis has an unappealing aroma [28]—reduce the likelihood that individuals pursue it for non-medical or otherwise inappropriate reasons. Nevertheless, some participants reported that physicians assumed they were seeking prescribed cannabis to get high, reflecting the underlying stigma towards cannabis use and those who seek it for medical reasons.

Appropriateness of cannabis products

Participants emphasized the importance of prescribed cannabis meeting patients’ needs. Concerns were particularly raised about the limited range of only five available strains, with many questioning whether these would be effective for their specific conditions. These findings align with international research indicating that medicinal cannabis users value being able to choose from divers strains and product forms, such as oils and edibles [39]. Many of our participants were consequently reluctant to seek prescribed cannabis in its current form, supporting Levesque and colleagues’ argument that access to services perceived as low-quality or ineffective constitutes a restriction of access to care [29]. The availability of non-prescribed cannabis at Dutch coffeeshops, which offer a greater variety of strains, further diminishes the incentive to pursue a prescription. In contrast, countries such as Germany and the United Kingdom provide over 150 strains of herbal cannabis through medical channels [44, 53]. Jurisdictions like Australia, Canada, and parts of the United States offer access to multiple forms, including extracts, therapeutic vapes, and oral preparations such as oils, edibles, and capsules [54–56]. Expanding the variety of prescribed products and strains in the Netherlands could enhance alignment with patient needs and improve both patient satisfaction and treatment outcomes.

Stigma

Stigma surrounding cannabis use emerged as a significant sociocultural factor shaping the acceptability of prescribed cannabis. Despite more than two decades of legal availability and a growing body of evidence supporting the therapeutic use of cannabis [17, 57–61], our interviews revealed that prescribed cannabis continues to be a stigmatized medicine within both the healthcare system and broader societal context. It is important to note that the sale of non-prescribed cannabis remains illegal in the Netherlands and is merely tolerated within licensed coffeeshops under Dutch policy. This ambiguous policy landscape contributes to the ongoing perception of cannabis as a substance of abuse. The persistent stigma influences how individuals believe they are perceived by others, ultimately shaping their decisions about whether to seek a prescription.

Participants noted that obtaining a prescription could help legitimize their use and affirm their identity as patients rather than illicit drug users. However, negative attitudes and stigmatization from healthcare providers and society deterred many from pursuing a prescription. These findings align with international research showing that stigma and judgment from physicians—both anticipated and experienced—discourage patients from requesting prescribed cannabis [37, 40, 41, 62]. Education and training for healthcare professionals should therefore address not only knowledge gaps, but also stigma reduction and the importance of empathetic and non-judgmental communication, as this can enhance patients’ willingness to discuss sensitive topics such as cannabis use [63].

Limited information and misinformation

Our findings also highlight informational barriers to accessing prescribed cannabis. Participants reported difficulty accessing trustworthy information from official sources. Instead they frequently relied on informal sources, which provided information that was inaccurate, outdated, incomplete, or biased. As a result, interview data revealed that participants often lacked knowledge or were misinformed about prescribed cannabis, which in turn hindered them from being able to make informed decisions about seeking care. Some participants also received wrong information about eligibility criteria and prescribed products from physicians, further compounding misinformation. Studies from other countries document similar challenges, including difficulties in accessing accurate information about prescribed cannabis and the prevalence of misinformation, particularly on the Internet [64–66]. There is a clear need for accessible, evidence-informed patient resources that address common questions and concerns in a transparent and user-friendly manner. Such resources could enhance the approachability of prescribed cannabis and empower patients to make informed decisions.

Access to care: an interplay of factors

Access to prescribed cannabis is the result of a complex interplay of financial, service-related, regulatory, informational, and sociocultural factors. Although we presented the five dimensions as separate from one another, in practice they are interconnected. For instance, participants’ limited knowledge about price, product range, and eligibility criteria influenced whether they perceived prescribed cannabis as affordable, appropriate for their needs, or even available to them. Concerns about the suitability of cannabis products deterred some individuals from seeking a prescription, even when they were eligible, as they felt that paying a higher price for a lower-quality product would ‘not be worth it’. Similarly, limited physician knowledge and stigmatizing attitudes shaped expectations of the quality of care, thereby reducing willingness to engage with the formal healthcare system. These interactions illustrate that barriers to accessing prescribed cannabis cannot be fully understood in isolation, and interventions to improve access should therefore adopt a multidimensional approach.

Implications for policy and clinical practice

Participants in this study generally indicated a preference for prescribed cannabis, provided it met their therapeutic needs, acknowledging its advantages over non-prescribed alternatives in terms of safety and medical oversight. This underscores that barriers to accessing prescribed cannabis in the Netherlands are systemic rather than rooted in a lack of patient interest. Aligning policies and medical guidelines with emerging evidence, while actively engaging patients in shared decision-making, will be essential for fostering appropriate and patient-centred use of medical cannabis. While medical cannabis policies have evolved rapidly in many countries in recent years, those in the Netherlands have remained largely unchanged since the legalization of medical cannabis. Based on the findings of this study, policymakers could consider reforms and targeted interventions such as expanding health insurance coverage, enhancing physician education, diversifying the range of available cannabis products, reducing stigma among healthcare professionals, and improving the availability of information about prescribed cannabis.

As more countries legalize medical cannabis, there is an opportunity to learn from different regulatory, clinical, and service delivery models. A key dimension is the access pathway. In Germany and Australia, for example, telehealth clinics have been introduced to facilitate access. While these models increase accessibility, they are now under scrutiny due to concerns that they may be targeting recreational users [67, 68]. This underscores the need to carefully balance facilitating access with preventing inappropriate prescribing. Similarly, eligibility criteria vary internationally. Some jurisdictions restrict access to a defined list of conditions, which can streamline access for some patients but exclude other patients entirely. In contrast, the Dutch system formally permits prescriptions for any condition, including psychiatric conditions, and in practice, cannabis is indeed prescribed to some individuals for depression, anxiety, and PTSD [7]. Yet, overall, access remains limited, suggesting that permissive policy frameworks alone are insufficient without clinical support.

Another area where models diverge is product diversity. Comparative analyses could examine how the range of available products influences patient outcomes and potential harms. For example, jurisdictions with a wide product selection might face more harms, such as accidental overdoses from edibles, but also potentially achieve higher patient satisfaction by allowing individuals to tailor treatment to their needs or preferences. In the Netherlands, participants considered the availability of only five prescribed strains as insufficient. By contrast, some countries offer more than 150 prescribed strains, raising questions about how physicians navigate prescribing with such extensive choice [44, 53]. Furthermore, the Dutch experience illustrates that long-standing availability of prescribed and non-prescribed cannabis does not automatically reduce stigma. Understanding the factors that shape physicians’ attitudes and developing strategies to reduce stigma will be essential for improving access. Systematic international comparison of access models could generate insights to inform policies that balance accessibility, safety, and patient satisfaction.

Limitations

This study has several limitations. First, the use of convenience sampling, along with potential researcher bias in participant selection, may have limited the representativeness of the findings. For instance, there may be an overrepresentation of certain perspectives, an underrepresentation of harder-to-reach groups, or limited variation in demographic or medical profiles. However, the results are broadly consistent with previous research, lending support to the validity of the conclusions. Second, interviews were conducted online to facilitate nationwide participation and reduce participation barriers. While this approach enhances accessibility, it may hinder rapport-building between the researcher and participants [69]. This may especially be an issue given the stigmatizing nature of medicinal cannabis use. To mitigate this, interviewers received extensive training to enhance their sensitivity to the topic and promote trust with participants during the interviews. Third, the study employed a specific theoretical framework to guide data collection and analysis. While this framework provided a structured lens for examining barriers, other frameworks or models may also have been appropriate and could offer additional or alternative insights from the data. Fourth, the focus was primarily on barriers related to the dimensions of accessibility, rather than on the corresponding population abilities defined in the framework. Consequently, the study highlights systemic barriers more than patient-level competencies for accessing care. Future research could explore how individual abilities interact with systemic factors to influence access and develop interventions that empower patients to navigate these barriers.

Conclusions

This study provides an in-depth exploration of barriers limiting patient access to prescribed cannabis in the Netherlands. Despite its legal availability for over two decades, access remains restricted by financial, service-related, regulatory, informational, and sociocultural factors. Key barriers include the perceived high cost of prescribed cannabis, the limited availability of prescribing physicians, restrictive medical guidelines, a lack of accurate and accessible information, the perceived poor fit between services and patient needs, and persistent stigma. Although the Dutch prescribing framework was designed to allow compassionate use of pharmaceutical-grade cannabis, many patients are compelled to rely on unregulated sources, exposing them to potential health, financial and legal risks. These findings underscore the urgent need for targeted and coordinated policy reforms and healthcare responses. Implementing an evidence-informed, patient-centred approach that addresses both systemic barriers and individual patient needs could enhance equitable access, ensure that prescribed cannabis meets therapeutic needs, and support safe and effective use of medical cannabis.

Supplementary Information

Below is the link to the electronic supplementary material.

Abbreviations

CBD

Cannabidiol

I

Interviewer

NHG

Nederlands Huisartsen Genootschap (Dutch College of General Practitioners)

P

Participant

THC

Tetrahydrocannabinol

Author contributions

LS designed the study. NG and LS conducted the interviews. NG and TM coded the transcripts. TM, NG and LS analysed the data and developed the themes. AF contributed to the development of the interview guide and the development of themes. BHW reviewed the themes and provided methodological guidance throughout. LS drafted the manuscript in consultation with NG, TM, AF and BHW. All authors read and approved the final manuscript.

Funding

This research study was funded by Bedrocan International B.V. The funder had no role in the design, data collection, data analysis, and reporting of this study.

Data availability

The dataset generated and analysed in this study is not publicly available to protect individual privacy. However, it can be obtained from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

The study was granted an exemption from ethics from the Medical-Ethical Review Committee METC NedMec (22-912/DB) and was evaluated and approved by the Trimbos Institute Ethical Review Committee (registration number 202213). Before scheduling interviews, participants provided written consent via an online form. They were first asked to read a Participant Information Statement and then indicate their consent by checking a box. Consent was reconfirmed orally at the start of each interview.

Consent for publication

Not applicable.

Competing interests

Alex Fraser, lived-experience partner in this research, is a patient advocate and works as Patient Access Lead at Grow Pharma, where he supports patients in accessing prescribed cannabis medicines in the United Kingdom. The other authors declare no competing interests.