Cannabis Legalization and Psychiatric Disorders: Caveat “Hemp-tor”

Rates of cannabis use in Canada are among the highest in the Western world. Past year use among Canadian youth is estimated to be approximately 25%,¹ with up to 28% of children aged 11 to 15 years reporting cannabis use, the highest rate among developed countries.² Moreover, 43% of Canadians currently endorse lifetime cannabis use.³ In contrast, rates of cannabis use disorder (CUD) appear to be lower (∼2.0–2.9%^4,5) but may be increasing.⁶ The scientific literature suggests that people with mental health and addictive disorders have higher rates of cannabis use and CUD compared to the general population.^7–9 While it is not clear whether chronic cannabis use is detrimental to physical health and may in fact have some modest benefits,¹⁰ cannabis use is known to be associated with lower motivation¹¹; problematic co-use of alcohol, tobacco, and opioids⁸; and poorer psychiatric outcomes notably in people at risk for or with pre-existing psychosis^12,13 and in people with mood and anxiety disorders.¹⁴ In Canada, the federal government is moving ahead with plans to effect the legalization of cannabis nationwide, which is scheduled to begin in July 2018.¹⁵ There are some notable potential benefits to this nationwide policy change, including a reduced burden on law enforcement and increased tax revenues.¹⁵ However, there are considerable concerns that the legalization of recreational cannabis use may be detrimental to vulnerable populations such as those with mental health and addictive disorders and to youth. It is also clear that more data are needed to assess the impact on these populations.⁹ Accordingly, the collection of such data before and after cannabis legalization is imperative if we are to understand fully any consequences of a national policy change such as cannabis legalization. Moreover, it is well known that children begin to first use cannabis during adolescence when most psychiatric disorders also have their onset.¹ Furthermore, there is preliminary evidence that cannabis legalization in the United States may increase youth access¹⁶; after legalization, Washington State experienced an increase in cannabis use among students in Grades 8 and 10 (cannabis use prevalence in Grade 12 students already exceeds 20%).¹⁶ This may be related to a reduced perception of cannabis risk,¹¹ and therefore, efforts to increase knowledge about the risks of cannabis in the general public, and youth in particular, are of paramount importance. As such, this information would have clear implications for the mental health of young people. Moreover, in American states that have approved commercial sales of cannabis, rates of cannabis use and CUD have increased compared to states that have not approved commercial cannabis sales.¹⁷ This perspective article reviews the topic of cannabis legalization and psychiatric disorders (including substance use disorders) and provides a framework for clinicians and policy-makers to approach these concerns going forward. We discuss an approach to these issues under the following subheadings:

1. A Clear Need for a General Population Education Strategy: Canadians need a broad-based public education strategy coordinated by the federal government to educate the general public about the advantages and disadvantages of recreational cannabis legalization that embraces a public health perspective. Potential benefits of legalization include reduced burden on law enforcement, increased tax revenues and reducing the stigma associated with cannabis use, and the potential to curtail black market availability of higher potency tetrahydrocannabinol (THC) cannabis formulations. Potential concerns include reducing the perception or risk of cannabis and resultant increases in cannabis use prevalence (and of CUD), the lack of roadside tests for cannabis-related driving impairment,¹⁸ and increases in high-potency THC cannabis in the black market, which might expand, given the regulation of THC content in a legalized recreational cannabis use framework. To date, such efforts have not been apparent. Recreational cannabis legalization is a complex issue, and strong arguments can be made on both sides, making the availability of evidence-based education critical. Moreover, given the concerns about cannabis and pregnancy, brain development, and fetal and child well-being,¹⁹ there is a clear need for a strategy directed to children and their parents, perhaps best accomplished through schools and supported by local and provincial governments. Previous attempts at drug prevention that utilized “scare tactics” (e.g., the US-based Drug Abuse Resistance Education [“DARE”] program) have been unsuccessful.²⁰ Recommendation: Create a national strategy for public education about the benefits and risks of cannabis and its constituents based on the available evidence that promotes open and sensible conversations on the topic and ensures that such information is updated on a regular basis.

2. Limits on THC Potency and Clearer Product Labelling: The National Working Group on cannabis legalization in Canada²¹ has clearly articulated the need for accurate product labelling, given the dose-dependent association between THC (the addictive component of cannabis) content and adverse events,¹¹ including to children,²² but the potential dangers as it relates to people with mental illness need to be clearly emphasized by mental health and public health agencies at local, provincial, and national levels. This is especially true, given that, at present, cannabis products available to the public are not clearly labelled in terms of cannabinoid constituents.²³ Recommendation: A robust program of public and physician education is needed about the risks of high THC products for youth and those at risk for or diagnosed with mental health conditions.

3. Minimal Age for Legal Recreational Cannabis Use: This age limit clearly needs to be science-based and at least be consistent with the legal drinking age (e.g., 19 years across Canada), as brain development continues into an individual’s mid-20s (of note, the Canadian Medical Association has suggested a minimum age of 21 years). Moreover, increases in the legal age for alcohol²⁴ and tobacco²⁵ are associated with reduced prevalence and the mitigation of morbidity and mortality, including that related to tobacco-related medical illness and alcohol-related automobile accidents. The Adolescent Brain Cognitive Development study, a large longitudinal study on the effects of cannabis on brain development funded by the US National Institutes of Health, will clarify issues regarding higher age restrictions, as adolescents in this study will be followed from ages 9 to 10 years and then again at ages 19 to 20 years, which should inform a science-based determination of a minimal age for legal cannabis use. Similar Canadian longitudinal studies in adolescents, such as the Saguenay Youth Study,²⁶ should receive ongoing research support. Recommendation: Convene a national working group of physicians, scientists, and policy-makers to regularly review the scientific evidence and data on longitudinal health outcomes after legalization to provide guidance on adjustments to the legal age limit for recreational cannabis use.

4. The Need for a National Surveillance Strategy Before and After Cannabis Legalization: There is much at stake here, and a pre-post legalization surveillance approach needs to be robust and comprehensive. For example, what will happen to rates of cannabis-related impaired driving after legalization? There is evidence from Colorado that rates of impaired driving have increased since the institution of commercial cannabis laws in that state.¹⁸ Moreover, if the prevalence of cannabis use increases, will that translate to increases in the rates of problematic use, such as CUD? Also, what will happen to rates of new-onset psychiatric disorders, such as mood, anxiety, and psychotic disorders, which are known to be exacerbated by persistent cannabis use?⁸ Thus, it is critically important that we collect such systematic data before and after cannabis legalization. Recommendation: There should be a system developed for the regular and accurate monitoring of health outcomes and cannabis use prevalence data, which can be used to inform subsequent evidence-based real-time policy decisions with respect to Canada’s cannabis legalization framework.

5. Developing an Enhanced Treatment Capacity for Problematic Cannabis Use Including Those With Psychiatric Disorders: Should rates of cannabis use, and CUD, increase after legalization, there will be a need to provide treatment to those who seek help for problematic use. Without further resources for this purpose, this will place an additional burden on the addiction (and mental health) treatment system. It is clear that comprehensive addiction and mental health policy and financing strategies will be needed to account for the expected effects of cannabis legalization, especially given the lack of proven benefits and high risks associated with cannabis use in people with psychiatric disorders.^8,9,27 Moreover, additional investment in the development of novel and effective pharmacological and behavioural treatment strategies for CUD is imperative.^8,28 Recommendation: Investment of resources into treatment development and provider capacity building to provide meaningful strategies aimed at addressing problematic cannabis use is of critical importance to the health and well-being of Canadians.

6. The Role of Physicians in Endorsing “Medical ” Cannabis and the Need for Provider Training: There has been considerable economic interest in the potential of therapeutic cannabis, and the commercial cannabis industry has moved quickly to position itself in the context of legalized recreational cannabis. The evidence supporting the therapeutic effects of cannabis and its constituents (e.g., THC, cannabidiol) is developing, but to date, high-quality evidence for the therapeutic effects of cannabis is only present for chronic pain, neuropathic pain, and spasticity associated with multiple sclerosis.²⁷ Knowledge among health professionals, especially physicians, is lacking about the evidence base for therapeutic effects of cannabis and needs to be developed and supported using a national strategy. Figure 1 provides an algorithm to guide physicians on how they might approach a patient seeking to use recreational cannabis and the steps involved in developing a rational clinical assessment and monitoring framework for clinical practice in the post-legalization era. Recommendation: Provide robust medical education for physicians at medical school and postgraduate education and continuing medical education levels about the science of cannabis and its potential therapeutic effects so that physicians can provide evidence-based advice and care to patients wishing to use recreational and medicinal cannabis.

Figure 1.

An algorithm for physicians advising their patients about cannabis.

Conclusions: Caveat “Hemp-tor”

There are strong reasons to approach cannabis legalization cautiously, given that long-term mental health outcomes in Canada may be impacted. Canada already has one of the highest rates of cannabis use, and CUD, in the Western world, and the legalization of cannabis for recreational purposes may increase this burden. Whether this translates into an increased burden to people at risk for, or with existing mental health and substance use disorders, is not clear. Data from the first US states that have legalized cannabis for recreational use (e.g., Colorado, Oregon, Washington, and Alaska) and other countries that have pursued cannabis legalization (e.g., Portugal and Uruguay) are unclear with respect to the mental health impact and may not yield firm conclusions for several years.^9,29 Nonetheless, given what we know about the effects of cannabis and mental health, it is clear that the consumer, physicians, health care policy-makers, and government officials need to be sensitive to these concerns. To these ends, we need robust monitoring of health outcomes and capacity to provide treatment to people who develop problematic cannabis use, perhaps funded by taxes on sales of recreational cannabis and mandatory contributions from companies profiting from cannabis. Ultimately, we need to be aware of the unintended consequences of cannabis legalization for these vulnerable populations: caveat “hemp-tor”!