Long-Term Health Outcomes of People with HIV Engaged in Chemsex: A Prospective Cohort Study on Drug Use, Sexual Behaviour, Sexually-Transmitted Infections and Vulnerability

Abstract

Introduction

Chemsex, the intentional use of drugs to enhance sexual experiences among gay, bisexual, and other men who have sex with men (gbMSM), is linked to high-risk sexual behaviours and increased sexually transmitted infections (STIs). Data on its long-term evolution after implementing specific strategies in HIV settings are limited. We evaluated the incidence of drug use, sexual behaviour, STIs, and vulnerabilities over 3 years following a specific approach at the HIV Unit of Hospital Clinic in Barcelona, Spain.

Methods

We included 209 gbMSM living with HIV who engaged in chemsex in a prospective cohort (2018–2022). Quarterly visits assessed sexual behaviours, drug use, and STIs screening. Data were collected via self-administered questionnaires, medical records, and microbiological tests. Statistical analyses included descriptive statistics and Poisson regression models.

Results

Chemsex incidence decreased significantly (IRR 0.88, 95% CI 0.83–0.92, p < 0.001). People engaging in intravenous drug use (slamming) decreased in year 2 (IRR 0.71, 95% CI 0.52–0.98, p = 0.037) but rose non-significantly in year 3 (IRR 0.86, 95% CI 0.60–1.25, p = 0.434). High-risk sexual behaviours persisted, specifically unprotected anal sex (IRR 1.02, 95% CI 0.96–1.08, p = 0.481) and unprotected fisting (IRR 1.20, 95% CI 1.05–1.39, p = 0.010). Syphilis cases declined (IRR 0.40, 95% CI 0.26–0.60, p < 0.001). At baseline, 29% had HCV antibodies, with five new acute HCV cases. Concerns about chemsex decreased (IRR 0.52, 95% CI 0.43–0.63, p < 0.001), whereas the demand for sexuality-related assistance increased (IRR 1.53, 95% CI 1.20–1.94, p = 0.004).

Loss to follow-up (21%) was greater among younger individuals, people engaging in intravenous drug use (slamming) (IRR 2.43 95% CI 1.33–4.42, p = 0.004), detectable HIV viral load (IRR 3.01, 95% CI 1.57–5.76, p = 0.001), and greater need for help (IRR 1.35, 95% CI 1.03–1.78, p = 0.03). Migrants and sex workers had higher rates of syphilis, lower education levels, and increased prevalence of STIs.

Conclusion

Chemsex incidence and syphilis rates declined, but persistent high-risk behaviours, subgroup vulnerabilities, and increasing demand for sexuality-related assistance require targeted interventions and comprehensive support.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40121-025-01201-7.

Plain Language Summary

This study investigated chemsex, which refers to the use of drugs to enhance sexual experiences among gay, bisexual, and other men who have sex with men (gbMSM) over 3 years at the HIV Unit of Hospital Clinic in Barcelona, Spain. The goal was to determine how drug use, sexual behaviour, sexually transmitted infections (STIs), and other vulnerabilities changed after the implementation of a specific care approach. The study followed 209 gbMSM living with HIV engaged in chemsex. Every 3 months, the participants completed questionnaires on substance use, sexual behaviours, and concerns, and medical tests were conducted. The results revealed that the number of people engaging in chemsex decreased over time. Most drug use decreased, except for mephedrone, a stimulant drug. Slamming, or injecting drugs in this context, also decreased in the second year but rose slightly in the third year without reaching significant levels. The number of syphilis cases decreased and only a few new cases of hepatitis C were found despite the continuation of risky sexual behaviours. Concerns about engaging in chemsex diminished, although people who still needed help asked for support related to their sexuality. Migrants and sex workers had higher rates of syphilis, lower education levels, and more STIs. Younger people and people who use intravenous drugs were more likely to be lost to follow-up. In conclusion, while the rates of chemsex and syphilis declined, risky sexual behaviours and vulnerabilities remained. More support and targeted health programs are needed to help those facing specific vulnerabilities.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40121-025-01201-7.

Key Summary Points

Why carry out this study?

To assess the longitudinal impact of a structured management approach for chemsex among gbMSM living with HIV at the HIV Unit of Hospital Clinic in Barcelona, Spain, addressing a gap in evidence from long-term follow-up.

Chemsex is associated with high-risk sexual behaviours and increased STI incidence among gbMSM living with HIV, yet little has been known about how these patterns evolve over time under dedicated clinical intervention.

What was learned from the study?

The incidence of chemsex and syphilis rates decreased significantly, although high-risk sexual practices persisted, as did the need for help with sexuality.

Loss to follow-up was greater among younger participants, those who engaged in slamming, and individuals with detectable HIV viral load. Other vulnerabilities were identified in migrants and sex workers.

The findings underscore the importance of targeted interventions and comprehensive sexual health support for general chemsex practices and the identified vulnerable subpopulations.

Introduction

Chemsex is defined as the intentional consumption of drugs prior to or during sexual intercourse by gay, bisexual, and other men who have sex with men (gbMSM) to facilitate, enhance, and extend sexual intercourse [1]. It is distinguished by the use of various drugs with stimulant, euphoriant, and dissociative effects that are used to increase desire and disinhibition and enhance sexual experiences [2] and that are associated with sexual risk behaviours [3, 4]. People who engage in chemsex are at a higher risk of sexually transmitted infections (STIs), including HIV and HCV [5, 6]. Chemsex may have detrimental long-term effects on mental health and may lead to increased rates of depression, anxiety, and substance use disorders [5].

The prevalence of chemsex among gbMSM ranges from 3% to 32% [7]. According to the European EMIS research in 2017, Spain is one of the countries with the highest prevalence of chemsex, with the most reports in Barcelona and Madrid [8]. Descriptive cross-sectional studies have been conducted in this context to evaluate the relationship between chemsex practices and STIs and other health conditions [9, 10]. Studies that identify specific vulnerable situations that require more specific approaches [11] and various qualitative studies that describe, for example, factors associated with practices, perceptions of health impact, and prevention needs [12] have been published in Spain.

There are only two international prospective cohort studies on chemsex, neither of which is based in Spain. The AURAH2 longitudinal study from the UK followed an HIV-negative cohort for 3 years [13], whereas an observational prospective cohort study in Hong Kong, which was based on an online survey, had a shorter, 6-month follow-up and focused on the impact of social media and apps aimed at gbMSM [14].

Additionally, various harm reduction strategies have been implemented in different settings, including HIV clinics, nongovernmental organizations (NGOs), and addiction units [15, 16]. However, these interventions generally have short follow-up periods and employ heterogeneous approaches with a primary focus on reducing substance use. This study advances prior research by focusing on people living with HIV (PWH), integrating a structured clinical approach, and providing longitudinal data.

Professionals in nonspecialized substance use settings, such as HIV clinics, STI services, and preexposure prophylaxis for HIV (PrEP) programs, have the opportunity to identify individuals who engage in chemsex with diverse consumption patterns because these settings involve sexual health conditions that are reported to be more prevalent in the context of chemsex [6]. Standardized and specific follow-up of these individuals in such settings is essential, not only to monitor HIV and STIs but also to address substance use, sexual practices, and psychosocial needs while establishing structured referral pathways to specialized care [17]. Understanding the risks, prevalence, and long-term consequences of chemsex is critical for developing effective therapeutic and support strategies.

The primary aim of this study was to evaluate the incidence and evolution of chemsex practices over 3 years among PWH who were followed in a tertiary hospital in Barcelona, Spain. This included assessing sexual behaviour, drug use, and the prevalence and incidence of STIs within this population and integrating a structured clinical approach into routine HIV care visits. As secondary objectives, we examined the factors associated with loss to follow-up, the prevalence of referrals and links to specialized substance support services, the evolution in vulnerable subgroups, and the progression of HIV-associated factors.

Methods

Study Design and Setting

This prospective cohort study recruited PWH who engaged in chemsex at the Hospital Clinic of Barcelona (HCB) from February 2018 to December 2019 with a 3-year follow-up to December 2022. The present study adhered to the ethical principles set forth in the Declaration of Helsinki from 1964 and its later amendments and followed all principles of good clinical practice. Ethics approval was previously obtained from the local research ethics committee from Hospital Clínic of Barcelona for the CSC Study (HCB/2017/0909) and funded by an international grant from ViiV Healthcare through its Positive Pathways program. All participants signed an informed consent form consenting to the study and further use of data.

Participants and Methods

The inclusion criteria included PWH and gbMSM over 18 years of age with a history of intentional substance use to enhance sexual intercourse at least once a month during the previous 6 months and/or more than 10 times in the previous year. Participants who met the inclusion criteria were informed, and those who agreed to participate signed the informed consent form. Participants who used drugs for nonsexual purposes were excluded. Participants were recruited from the HIV clinic, the emergency department, the psychiatry department, the STI consultation, and a local NGO named STOP.

Visits were performed every 12 weeks by a nurse and a physician, following the existing recommendations for individuals engaging in high-risk behaviours for STI acquisition. At each visit, syphilis (VDRL) and IgG-HCV serologies were requested (HCV-RNA if the person had a previous positive IgG), as were multiple STI PCRs (Chlamydia trachomatis (CT), Mycoplasma genitalium (MG), Neisseria gonorrheae (NG)) in the urine, pharynx, and rectum. A general assessment of HIV infection was conducted every 6 months, with more frequent monitoring if the HIV viral load was detectable.

Each quarterly visit included self-administered coded electronic questionnaires on drug use, sexual practices, and the perceived need for support services to ensure confidentiality and promote honest responses. While the questionnaires were not formally validated, they were piloted with a subset of participants, expert committee, and professionals from the NGO STOP for clarity and relevance.

As part of routine clinical practice, each visit included a specific assessment of drug use, risk reduction strategies, adherence to medication, potential drug interactions, concerns and perceived needs related to substance use, and the possibility of referral for psychiatric or psychological support.

Variables

We included in the analysis demographic and social variables (place of birth, educational level), sex work (variable added in January 2020), substance use (type of drug, polydrug use, administration and frequency of use, concerns and need for help), sexual practice behaviours, and HIV-related characteristics (viral load and CD4).

The microbiological parameters (STI PCR) were recorded via an electronic case report form (eCRF) implemented in the REDCap system [18] hosted at the Hospital Clinic of Barcelona. This eCRF was specifically designed for this study. Data on sexual practices and drug use were collected through e-surveys integrated into the eCRF, while HIV-related variables were retrieved from the electronic medical records of our center.

Statistical Analysis

Qualitative variables are presented as frequencies and percentages, and quantitative variables are presented as means and standard deviations (SDs) or medians and interquartile ranges (IQRs). The evolution of the observed variables over the quarterly visits was visualized using plots. To estimate the early incidence rate (IR) of each variable and compare it with the baseline value (expressed as the incidence rate ratio (IRR) and its 95% confidence interval), a Poisson regression model with clustered standard errors on participants was applied. All tests were two-tailed, and the significance level was set at < 0.05. The statistical software used was Stata version 17 [19].

Results

Out of 304 people who met the inclusion criteria, a total of 209 people were included, of whom 67% (n = 141) completed the follow-up at 3 years. Figure 1 shows the flowchart of the included population. The mean age of the included participants was 38 years; 51% (106/209) were Latin American, and 43% (81/190) had a university education.

Fig. 1.

Flowchart

Sexual Contacts

During the follow-up, the median number of sexual partners in the previous 3 months remained stable in the range of 30–53 contacts. However, the percentage of traceable sexual partners decreased significantly over 3 years, with an IRR of 0.93 (p < 0.018) (Fig. 2). Between 10% (7/68) and 29% (7/24) of the participants reported sex work, with no difference during the study period. Most of them used drugs during sex work. (Further details are provided in the supplementary material.)

Fig. 2.

Sexual contacts. M months, Y year

Sexual Practices

Unprotected anal sex was highly prevalent throughout the study period, reported by 88–96% of those engaging in anal sex. Fisting, the colloquial term to refer to brachioproctic insertion practice, remained stable over time, with prevalence ranging from 40% to 57%. The tendency to use protection decreased, with a reduction in the practice of protected brachioproctic insertion (fisting), in year 2 (IRR 1.17, 95% CI 1.02–1.34, p = 0.03) and year 3 (IRR 1.20 95% CI 1.05–1.39, p = 0.01) of the follow-up. (Further details are provided in the supplementary material.)

Drug Use

Figure 3 illustrates drug use-related characteristics. Compared with the baseline visit, the incidence of chemsex decreased significantly over the 3 years of follow-up (IRR 0.88 95% CI 0.83–0.92, p < 0.001), with significant reductions in all drug use except mephedrone use during the third year (IRR 0.70, 95% CI 0.57–0.86). (More details in supplementary material.)

Fig. 3.

Drug-related characteristics. a Drug use. b Drug administration. c Frequency of drug use. d Concerns and need for help. M months, Y year, GHB/GBL gamma-hydroxybutyrate/gamma-butyrolactone, MDMA 3,4-methylenedioxymethamphetamine, Meth methamphetamine, Poppers amyl nitrite, Viagra sildenafil and derivatives, STI sexually transmitted infections

Most participants reported practicing chemsex on a weekly basis (between 30% (43/142) and 44% (37/85)) or monthly basis (between 26% (22/85) and 44% (63/142)). An increase in monthly use and a decrease in weekly use were observed, although these decreases were not significant except for a decrease in weekly use in the first year (IRR 0.81 95% CI 0.68–0.98, p = 0.029).

Slamming, the colloquial term to refer to intravenous drug use in the chemsex context, decreased significantly in the second year of follow-up (IRR 0.71 95% CI 0.52–0.98, p = 0.037) with an increasing trend thereafter that was not significant.

During follow-up, between 21% (25/119) and 38% (29/76) of the participants stated that they could not remember the last time they had had sober sex. In the second year of follow-up, there was a decrease in sober sex (IRR 0.90 95% CI 0.81–1.00, p = 0.049).

We found a significant decrease in concern about engaging in chemsex (IRR 0.52 95% CI 0.43–0.63, p < 0.001) during follow-up. However, among those who expressed concern and a need for help, the need for help with respect to chemsex practices increased from the baseline visit to become statistically significant in year 3 (IRR 1.20 95% CI 1.06–1.36, p = 0.004). The need for help related to consumption management increased (although not significantly) during the 3 years of follow-up, whereas the need for help related to possible STIs decreased in years 1 and 2, with an IRR of 0.87 (95% CI 0.76–0.99, p = 0.030) and an IRR of 0.78 (95% CI 0.66–0.92, p = 0.003), respectively. The need for help related to sexuality increased significantly in the third year of follow-up compared with baseline (IRR 1.53, 95% CI 1.20–1.94, p = 0.001).

Sexually Transmitted Infections

No significant changes were observed in the incidence of CT, with a cumulative incidence of 10% (IQR 6.4%, 14.8%) or MG infections throughout the study period. A significant decrease in NG infections was observed only during the second year of follow-up (IRR 0.59, 95% CI 0.41–0.83, p = 0.002) (Fig. 4). (More details are provided in the supplementary material.)

Fig. 4.

Sexually transmitted infections. M months, Y year, VHC hepatitis C virus

The cumulative incidence of syphilis at baseline was 19.7% (95% CI 14.3–25.1%), with a significant reduction during the entire study period (IRR 0.40 95% CI 0.26–0.60, p = 0.001).

We do not have data on postexposure prophylaxis with doxycycline (DoxiPEP) because it was not officially approved during the study period and we did not ask specifically about its use. This situation might have an impact on the trends of STI observed in our cohort.

At the first visit of the study, 29% (60/209) of the participants had a positive IgG-HCV; 25% (15/60) of them had active HCV infection with positive HCV-RNA. During the 3-year follow-up, five new cases of acute hepatitis C were diagnosed, none of which were reinfections.

HIV-Associated Characteristics

HIV control during follow-up remained stable with a median CD4 count above 600 cells/mm³ and a cumulative incidence of 14.4% (95% CI 9.6–19.1%) of participants with a detectable viral load at baseline. A significant decrease in the number of participants with detectable viral loads was observed during the first year of the study (IRR 0.62, 95% CI 0.39–0.98, p = 0.042) but was not maintained during the remainder of the study period. All of these participants were on antiretroviral therapy, and the detectable viral load was related to adherence to treatment. No virological failures were confirmed. Supplementary Table S1 provides more information about cumulative incidence and 95% confidence interval (CI) of sexual practice behaviours, substance use, sexually transmitted infections, and HIV viral load.

Referrals Performed

During the 3-year period, 61% (127/209) of the participants agreed and were referred to consumption management. Among these participants, 64% (81/127) underwent follow-up, and 70% (57/81) attended regularly. More information about referrals and follow-up can be found in Fig. 5.

Fig. 5.

Referral for consumption management. NGO nongovernmental organization

Evolution of Vulnerability Conditions

Loss to Follow-up

A 21% rate of loss to follow-up was noted throughout the course of the 3-year follow-up period; 77% represented actual losses, whereas the remaining 33% showed erratic follow-up patterns.

Notably, at baseline, participants lost to follow-up had lower levels of university education (10 (26%) vs. 29 (74%); p = 0.023)), were younger (mean age 35.00 (29.00; 44.00) vs. 38.00 (33.00; 43.00); p = 0.042), consumed more GHB (IRR 1.22, 95% CI 1.06–1.41, p = 0.007), were more likely to have detectable HIV viral load (IRR 3.004, 95% CI 1.57–5.76, p = 0.007), and reported a greater need for help with chemsex practices (IRR 1.28, 95% CI 1.000–1.62, p = 0.05).

Throughout the follow-up period, the participants engaged significantly more in intravenous drug use (slamming) (IRR 2.43, 95% CI 1.34–4.42, p = 0.004) and presented with more diagnoses of syphilis (IRR 1.76, 95% CI 1.20–2.60, p = 0.004).

During the follow-up, two deaths were reported, one due to cardiac arrest and the other due to lung-related cancer.

Migrant Participants

Migrant participants were significantly younger than Spanish participants (p < 0.001) and presented significantly more positive syphilis results (IRR 2.772, 95% CI 1.22–6.28, p = 0.02). During follow-up, migrant participants engaged significantly less in intravenous drug use (slamming) (IRR 0.47–95% CI 0.26–0.85, p = 0.01) but consumed more cocaine (IRR 1.46, 95% CI 1.02–2.08, p = 0.04).

Participants Engaged in Intravenous Drug Use (Slamming)

Participants with intravenous drug use were significantly older (p = 0.004), had positive HCV serology (IRR 1.935, 95% CI 1.27–2.95, p = 0.002), and used more mephedrone (IRR 1.76, 95% CI 1–2.27, p = 0.001) and methamphetamine (IRR 1.25, 95% CI 1.118–1.396, p = 0.001) at baseline. During follow-up, these participants used more methamphetamine (IRR 1.42, 95% CI 1.17–1.73, p = 0.001) and had more syphilis diagnoses (IRR 1.87 95% CI 1.26–2.77, p = 0.002).

Sex Workers

Sex workers were significantly younger (p = 0.001), were treatment-naive (p = 0.001) for HIV, had lower education levels, had more diagnoses of CT (IRR 2.60, 95% CI 1.17–5.85, p = 0.020), had fewer HCV diagnoses (IRR 0.24 95% CI 0.08–0.73, p = 0.012), and consumed less GHB/GBL (IRR 0.71, 95% CI 0.52–0.98, p = 0.039).

During follow-up, these participants continued to have more CT diagnoses (IRR 1.66, 95% CI 1.10–2.50, p = 0.016), consumed more cocaine (IRR 1.58, 95% CI 1.14–2.19, p = 0.006), had a higher percentage of detectable viral load (IRR 3.60, 95% CI 1.84–7.04, p = 0.001), and had higher rates of loss to follow-up. However, their rates of polydrug use (IRR 0.62, 95% CI 0.41–0.93, p = 0.007) and intravenous drug use (slamming) (IRR 0.34, 95% CI 0.13–0.92, p = 0.034) were lower.

Discussion

This study offers a unique contribution by employing a longitudinal design and an integrated care model to monitor chemsex-related behaviours and health outcomes among PWH over time. Unlike cross-sectional studies, our approach allowed us to capture the evolving patterns of drug use and STI risk, providing evidence to support concrete interventions such as integrating quarterly STI screening and addiction referral services into routine HIV care for individuals engaged in chemsex. In contrast, the AURAH2 prospective study focused on HIV-negative gbMSM in the UK, factors associated with HIV acquisition, changes in sexual behaviour, and fewer types of drugs and primarily utilized online questionnaires [13]. Despite these methodological differences, both studies underscore the prevalence of high-risk sexual behaviours and the complexity of drug use patterns in this context, which coincides with other studies [1].

In this study, we implemented a quarterly follow-up during routine HIV clinic visits that included surveys on drug use and sexual practices as well as a medical interview that specifically addressed substance use, behaviours, and a needs assessment. Additionally, we provided targeted referrals for substance use management to ensure a more comprehensive and individualized approach. Although a multidisciplinary approach to chemsex is recommended, there is little evidence of efficacy and long-term follow-up, as in this study. A recent systematic review of harm reduction strategies [16] revealed that interventions for chemsex among MSM include web-based programs, peer-led support, and mobile health services. Digital interventions, such as mindfulness-based cognitive approaches and harm reduction platforms, improve self-efficacy and promote safer practices, while peer-led programs, particularly those facilitated by individuals with lived experience, demonstrate greater engagement and abstinence rates. Mobile health initiatives, such as distributing safer sex and drug use kits, have also proven beneficial. However, these interventions typically have short follow-up periods and assess only specific actions, which differs from our broader, more comprehensive approach.

The mean age of the participants in this study was 38 years, and less than half of the participants had a university education. In contrast, a recent review on chemsex [7] suggested that individuals who engage in chemsex predominantly have higher socioeconomic status. Our cohort showed distinctive vulnerabilities that were previously reported [11]. Approximately half of the respondents experienced migration-related socioeconomic and psychosocial challenges.

High-risk sexual practices remained stable throughout the 3 years of follow-up, with a decreased tendency to use protection even for higher-risk sexual practices such as brachioproctic insertion (fisting) and a significant decrease in the percentage of traceable sexual partners. Our results differ from those of the AURAH2 study [13], which reported a significant decline in anal sex and group sex but an increase in unprotected anal intercourse with one or more partners. The stability of high-risk sexual practices reflects consistent behaviour in relation to chemsex, which is linked to the effects of psychoactive drugs that lower inhibitions [20, 21] and reinforced by social networks that facilitate these practices [22]. Our results also coincide with the findings of another study on increased rates of unprotected sexual practices and the rise in chemsex between 2016 and 2023 in Barcelona [23]. The anonymity of sexual partners [24] complicates contact tracing and increases the risk of undiagnosed STIs, which highlights the need for frequent STI screenings among individuals who practice chemsex [24].

With respect to STIs, we found a significant decrease in syphilis during the entire study and a significant reduction in NG during the second year, but no changes in CT or Mycoplasma infections were found. This finding aligns in part with the AURAH2 study [13], which revealed a significant decline in all bacterial STIs. Some of the discrepancies may be related to the stable high-risk sexual practices observed in our cohort. We did not ask about the use of DoxiPEP [25], which was not officially approved during the study period, nor did we specifically collect data on whether any participants were using it without an official medical prescription. This may represent a potential bias in the results. Despite the high prevalence of HCV in our chemsex cohort at baseline, only five new cases of acute hepatitis C were diagnosed during follow-up. In our unit, we previously reported a decline in incidence after 2017 [26], likely due to the universal access and efficacy of new oral antivirals. However, we observed an increase in HCV reinfections with 76% linked to chemsex practices, although this could not be fully assessed in the present study.

In this study, 14% of chemsex participants had a detectable viral load, which was more than twice the prevalence in our hospital cohort. This finding aligns with research linking chemsex to poor viral suppression due to inconsistent antiretroviral therapy (ART) adherence, which is influenced by psychosocial factors and substance use [27]. HIV care should prioritize adherence support through robust ART regimens with forgiving pharmacokinetics and minimal drug interactions. Long-acting injectable ART is a promising alternative for those who are well engaged in care [28], but data in this population are lacking. Our group is investigating this, although results are unavailable in this study because long-acting ART was not yet accessible in Spain during the analysis period.

We observed changing substance use patterns over the 3-year follow-up, with declining cocaine use, stable methamphetamine use, and increasing mephedrone use. This finding highlights the evolving nature of chemsex and the need for continuous monitoring of emerging substances. In contrast to the USEX Study 2, which compared two cross-sectional studies in the Madrid community between 2016–2017 and 2019–2020, no significant differences were found in the types of substances used [10]. This reinforces the understanding of the temporal and geographical variability of the phenomenon, even within the same country. In our study, chemsex practices decreased by 10%, with a trend shift from weekly to monthly chemsex episodes. While this reduction was less pronounced than it was in the AURAH2 study, our findings support the value of integrated care models [15, 17, 29].

The participants reported fewer concerns about chemsex and less need for STI-related support, likely due to our structured and more comprehensive approach. However, by the third year, there was an increased demand for sexual health support and an increase in the number of participants who did not have sober sex. A qualitative study [30] suggested that this may be linked to the perceived benefits of chemsex, such as heightened arousal and prolonged encounters, in addition to evolving motivations such as coping with stress and sexual difficulties. These findings emphasize the need to integrate discussions about sexual health into chemsex care strategies.

Half of our participants were referred to addiction treatment services or NGOs, and approximately half of the participants referred engaged consistently with these services. This finding highlights the need for clear interdisciplinary referral pathways to enhance linkage to care. However, our findings also suggest that not all chemsex practices lead to problematic outcomes [31], as previously recognized in the literature. HIV units, STI and infectious disease clinics, and PrEP services play key roles in identifying diverse chemsex patterns. Moreover, improving motivational interviewing skills is essential for accurately identifying and effectively referring those individuals who experience harmful consequences.

Our study identified several vulnerable subgroups that require targeted interventions. One in five participants were lost to follow-up, with higher risks observed among those with greater GHB use, intravenous drug use (slamming), concerns about consumption, and detectable viral loads. Re-engagement strategies must address barriers such as stigma, psychosocial complexities, and substance dependence [32].

Half of our cohort were migrants, a group that is particularly vulnerable because of sociocultural and structural factors. Many use chemsex as a means of social connection in unfamiliar environments but face compounded stigma from HIV and homophobia, which increases isolation and health risks [33]. Limited social networks further heighten the risk of substance dependence and poor health outcomes, reinforcing the need for culturally sensitive interventions that integrate harm reduction, mental health support, and social connection strategies [34].

Intravenous drug use (slamming) remained stable over the 3-year follow-up but was likely underreported because of stigma [35]. Unlike traditional intravenous drug users, people engaged in intravenous drug use in the chemsex context are often new to injection practices and require tailored harm reduction approaches because current interventions primarily target more established populations. They also experience a greater psychiatric burden, including depression and psychosis, particularly with synthetic cathinones and methamphetamine, which emphasizes the need for multidisciplinary care and early detection [36, 37]. Additionally, slamming is associated with polydrug use and high-frequency sessions, which increase the risks of addiction, overdose, and long-term health consequences [38].

Sex work was reported by 29% of the participants, with most using drugs while working. This group faces a syndemic of vulnerabilities, including multiple sexual partners, high mobility, and low self-esteem, which increase health risks [39–41]. Structural factors such as stigma and discrimination further hinder access to prevention and expose this population to violence. Younger age, migrant status, lower education, and higher rates of loss to follow-up further underscore their vulnerability and highlight the need for specialized follow-up.

Overall, these findings emphasize the need for targeted, multidisciplinary approaches tailored to the specific needs of each subgroup. Addressing these vulnerabilities through specialized interventions is essential for improving health outcomes and providing care in chemsex populations.

Limitations

This study has several limitations. Its observational design prevents causal inferences, and external factors—particularly the COVID-19 pandemic—may have influenced the findings. While lockdowns and social restrictions likely reduced opportunities for chemsex at certain points, high-risk sexual behaviours and substance use persisted throughout the study period. The overall impact of the pandemic on participant behaviour is difficult to quantify but should be considered when interpreting trends over time. Single-center recruitment may not fully represent the broader population of chemsex users, particularly those who do not access health care or those who declined participation. While a structured follow-up was conducted for the entire cohort, the absence of a control group limits direct comparisons.

Self-reported data on sexual practices and drug use may be affected by recall and social desirability biases. Additionally, the 21% loss to follow-up, primarily among participants with higher substance use and a detectable HIV viral load, poses a risk of attrition bias. Although the study assessed specific needs related to substance use, psychosocial and mental health factors, such as stigma and the underlying motivations for chemsex, were not comprehensively explored. Furthermore, the dynamic nature of drug use patterns highlights the need for continuous updates to intervention strategies.

Despite these limitations, this study provides valuable insights because it is the only longitudinal follow-up conducted in PWH who engage in chemsex utilizing a structured and integrated approach to address chemsex practices and related health outcomes. This model may be implemented in other HIV care settings to enhance comprehensive care and harm reduction strategies.

Conclusions

Decreases in the incidence of chemsex and syphilis cases in addition to persistent high-risk behaviours and specific vulnerabilities in subgroups (migrants, intravenous drug use (slamming), sex workers, and lost-to follow-up) underscore the need for targeted interventions. The increasing demand for sexuality-related assistance and adherence to follow-up care reflect opportunities for more comprehensive support strategies.

Supplementary Information

Below is the link to the electronic supplementary material.

Author Contributions

Lorena De La Mora and Montserrat Laguno contributed equally to the study. Josep Mallolas and Maria Martínez-Rebollar contributed equally to the study. Lorena De La Mora, Montserrat Laguno, Josep Mallolas and Maria Martínez-Rebollar designed the study. Duncan Short collaborated in the study design as a ViiV representative. Lorena De La Mora, Montserrat Laguno, Berta Torres, Iván Chivite, Alberto Foncillas, Ana González-Cordón, Alexy Inciarte, Juan Ambrosioni, Júlia Calvo, Esteban Martínez, José Luís Blanco, Jordi Blanch, Laia Miquel, Rubén Mora, Estela Solbes, Ana Rodriguez, Josep Mallolas and Maria Martínez-Rebollar recruited patients for the study. Josrdi Blanch and Laia Miquel assessed the follow-up from the Addiction Unit and Psychiatry service. Rubén Mora assessed the follow-up from NGO STOP. Pilar Callau was the data manager and the person in charge of linkage-to-care participants in the study. Lorena De La Mora, Montserrat Laguno, Leire Berrocal, Elisa De Lazzari, Pilar Callau, Josep Mallolas and Maria Martínez-Rebollar analyzed and interpreted the data. Lorena De La Mora, Montserrat Laguno, Josep Mallolas and Maria Martínez-Rebollar were involved in drafting the manuscript. All the authors were involved in reviewing the manuscript and approved the final version.

Funding

This work was supported by an international grant from ViiV Healthcare within its Positive Pathways program in support of the CSC study, including the journal’s Rapid Service Fee for this specific publication.

Data Availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Conflicts of Interest

Lorena De La Mora has received fees to give lectures from Gilead, MSD, ViiV, AbbVie and Janssen-Cilag. Montserrat Laguno has received fees to give lectures from Gilead, MSD, ViiV, AbbVie and Janssen-Cilag. Maria Martínez-Rebollar has received fees to give lectures from Gilead, MSD, ViiV, AbbVie and Janssen-Cilag. Berta Torres has received fees to give lectures from Gilead, MSD, ViiV, AbbVie and Janssen-Cilag. Juan Amborsioni has participated in advisory boards and received consulting honoraria, research grants, or both from Gilead Sciences, Janssen Pharmaceuticals, and ViiV Healthcare, all outside of this work. Alberto Foncillas has received fees to give lectures from Gilead and ViiV. Esteban Martínez has received honoraria for lectures or advisory boards from Gilead and Janssen, and his institution has received research grants from MSD and ViiV. Laia Miquel has received honoraria for lectures from Lundbeck, Gilead and Neuraxpharm. Jordi Blanch has received honoraria for lectures or advisory boards from Ferrer Internacional, Gilead, Janssen, MSD and ViiV. Ana González-Cordón has received fees to give lectures and participate in advisory boards from Gilead, MSD, ViiV, AbbVie and Janssen-Cilag. Alexy Inciarte has received educational grants from MSD and Gilead. José Luís Blanco has received honoraria for lectures or advisory boards from Gilead, Janssen, MSD. Iván Chivite has received fees to give lectures from Gilead, MSD, ViiV, AbbVie and Janssen-Cilag. Duncan Short is an employee of ViiV Healthcare and a shareholder of GlaxoSmithKline. Josep Mallolas has received honoraria, speakers’ fees, consultant fees or funds for research from MSD, Roche, Boehringer-Ingelheim, ViiV, Gilead, Janssen, BMS, and AbbVie. Estela Solbes has a research grant from Gilead. Elisa De Lazzari, Leire Berrocal, Ana Rodriguez, Pilar Callau, Júlia Calvo and Rubén Mora have nothing to disclose. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Ethical Approval

The present study adhered to the ethical principles set forth in the Declaration of Helsinki from 1964 and its later amendments and followed all principles of good clinical practice. Ethics approval was previously obtained from the local research ethics committee from Hospital Clínic of Barcelona for the CSC Study (HCB/2017/0909) and funded by an international grant from ViiV Healthcare through its Positive Pathways program. All participants signed an informed consent form consenting to the study and further use of data.