Effects of recreational cannabis versus black market: A randomized controlled trial in Switzerland (WEED CARE)
Background
Several countries have legalized cannabis for recreational use. Although population-based evidence from these countries is rapidly growing, data on the effects on cannabis misuse and related mental health outcomes are scarce. Furthermore, previous studies on the health effects of legal recreational cannabis have mainly been based on observational studies. However, inferences from these studies are limited. Therefore, we evaluated for the first time the impact of legal recreational cannabis compared to the black market on cannabis misuse and related mental health outcomes in cannabis users.
Methods
The WEED CARE study is a randomized controlled trial of six months with a subsequent observational study of two years in Switzerland. The study started in January 2023 and last until July 2025. Participants are adult (aged ≥18 years) cannabis users. Main exclusion criteria were current inpatient psychiatric treatment, acute psychosis or suicidality. Participants were randomly allocated to the intervention group with legal access to recreational cannabis in pharmacies (six cannabis products and safer use information) or the black market control group that had to continue to obtain their cannabis illegally. After six months all participants received access to legal cannabis. During the entire study period participants are asked to complete surveys about cannabis use, mental health outcomes and other substance use every six months.
Results
A total of 665 participants were screened for eligibility. 378 participants were randomly assigned - 189 to the legal cannabis intervention group and 189 to the black market control group. First results of the randomized controlled trial of 6 months will be presented, that are currently analyzed. Specifically, the effects of legal cannabis on cannabis misuse and related mental health outcomes compared to the black market will be shown.
Conclusions
Findings of the WEED CARE study shall contribute to an evidence base for decision making about cannabis policy.
