Mapping and mitigating the health risks of legalizing recreational cannabis use: a call for synergy between research and policy

In the past decade, a growing body of studies has been documenting the health risks of recreational cannabis use1. Short-term risks include (but are not limited to) impaired memory and psychomotor performance, and risky behaviors such as driving and working while intoxicated, which can result in car crashes and accidents at work. Long-term risks include adverse physical health outcomes (e.g., respiratory problems, testicular cancer, and abnormal fetus development), impaired cognitive performance and educational attainment, changes in brain integrity2, mental disorders (e.g., psychoses, depression, anxiety disorders, and bipolar disorder), and cannabis use disorders. Emerging evidence shows that the use of high-potency cannabis products, daily or almost daily use, and younger age at cannabis use onset exacerbate adverse health outcomes in recreational cannabis users3. Hall and Lynskey4 describe several pub­lic health developments which have oc­curred in US after the legalization of re­creational cannabis use. Cannabis products are more potent, cheaper and more available to adults. Adults are increasingly using the drug, and more of them are using it daily now. In emergency departments, more cannabis-related attendances and hospitalizations of adults, but also of adolescents and children, have emerged. The detailed review of recent studies shows that the legalization of recreational cannabis use poses (largely unmet) public health challenges. But do these surveys provide sufficient data to reveal “the full picture” so far? There are three reasons why this may not be the case. First, it is difficult to map the health effects of existing cannabis regulatory frameworks, as they have heterogeneous content and implementation and change at a different pace in distinct regions. This variability of conditions makes it difficult to interpret trends of changes in cannabis products, use levels and cannabis-related health problems within one state and hampers comparisons across jurisdictions5. Second, legalization is leading to a dynamic and broad cannabis market in the US. Many new products have become avail­able (e.g., edibles, oils, infusions, vapes, liquids, dabbing, home-grown cannabis). There is no consistent guidance, oversight or monitoring of their distribution and sale5. Therefore, the products’ content, quality, labelling and packaging control is uneven. There is no consistent agreed-upon mea­sure to systematically evaluate and compare their properties (e.g., serving size, potency and mode of administration). Consequently, the health risks of novel cannabis products are largely unknown. Third, “gold standard” measures of can­nabis exposure are lacking. Decades of research on cannabis use and related harms (and benefits) have been relying on heterogeneous and often somewhat superficial measures of exposure, e.g. binary definition of user vs. non-user that do not segregate dependent daily users from occasional non-problem users. Research lacks details on which cannabis products are used (e.g., dabs, edibles, liquids), how they are administered (e.g., joints, bongs) and levels of exposure (e.g., frequency, quantity). Further, household surveys have been evaluating the prevalence of cannabis use, misuse and related harms in normative samples. They have failed to represent hard-to-reach populations that might be more vulnerable to the adverse health risks of cannabis use (e.g., socially disadvantaged or marginalized groups). To sum up, the evidence on the health risk of legalizing recreational cannabis use is still inadequate. There is an urgent need for an improved evaluation of the novel public health challenges (and resources). But how can the situation be improved? We need a vision of an improved surveillance of cannabis-related risks in jurisdictions which legalized cannabis for recreational use – and beyond. Hereby, several public health strategies are suggested. First, we need to create an overarching framework. To systematically map regulatory frameworks, cannabis markets, trends in cannabis use and adverse health consequences, societies will need time and monetary resources. Governments may benefit from a multi-step approach on their way to establish systematic cannabis monitoring systems. In a first step, they can use information from existing resources, such as already available datasets6. In the medium term, large scale surveys within and across international jurisdictions with varying legal cannabis statuses could be run. In the long term, multi-country longitudinal surveys using consistent testing tools (“gold standards”) may be conducted to monitor different regulatory frameworks. Second, we need to involve key players, in order to bridge the gap between science and policy. International networks of scientists, stakeholders (e.g., medical profes­sionals, government agencies, public health organs, advocacy groups) and policy makers should come together and co-design the much needed “gold standard” measures of cannabis exposure. To keep up with the new challenges and resources of rapidly changing cannabis markets, new tools need to be developed to assess the properties and unknown health effects of new cannabis products. Third, we should use available key in­di­cators. For instance: a) socio-demographic characteristics of consumers (e.g., age, gender, socio-economic status) and socio-economic index of the area where cannabis is sold; b) regulatory framework; c) prevalence and patterns of cannabis use, including risk perceptions; d) problem cannabis use; e) adverse outcomes (e.g., problems from acute exposure, car crashes, working accidents, poison calls, mental and physical or social problems); f) treatment demand (e.g., emergency department visits, outpatient treatment, hospital admissions). Household and high school surveys can be used to get representative population data7. Information from colleges, universities and job centres, the criminal justice system, emergency departments, as well as mental health and addiction services, could also be used. To gain information on marginalized or hard-to-reach populations will be more difficult. New innovative search strategies need to be developed, requiring additional monetary resources. Fourth, we need to develop new key in­dicators. It is important to monitor the broad cannabis markets and to gain insight in the properties of novel cannabis products. New assessment instruments are needed to eval­uate cannabis product types, features and modes; potency (tetrahydrocannabinol con­tent), price, addic­tion liability, and adverse health outcomes. As suggested by Hall and Lynskey, sales volumes should be moni­tored too. Finally, cannabis research should be­come a top priority. Cannabis is the most widely used controlled drug worldwide, yet it remains largely understudied. To catch up with the new public health challenges posed by changing cannabis regulations, more research is needed. Significantly higher research budgets will be required to get high-quality studies, independent from the expanding cannabis industry. To facilitate research, regulatory barriers for the conduct of experimental studies will need to be removed. In conclusion, there is emerging evidence about cannabis-related risks, but knowledge about the effects of legalizing recreational cannabis use is still at an embryonic stage. Scientists, stakeholders and policy makers will need to join forces to address this gap.