Summary: The Weed Care study in Switzerland examines how regulated, legal access to cannabis affects patterns of use and mental health among adult consumers. In the first randomized controlled trial of its kind, participants given legal access to cannabis purchased through pharmacies showed a modest decline in problematic use, with the strongest benefit observed among people who also used other drugs. No increases in depression, anxiety, or other mental health symptoms were detected in the legal access group compared with those continuing to source cannabis from the illegal market. After six months, the control group was also offered legal access; interim results after two years indicate improved overall mental wellbeing among the study participants who remained in the trial.
The interdisciplinary Weed Care project started in January 2023 as a collaboration between cantonal addiction services, university researchers and psychiatric clinics in Basel and Aargau. The trial was designed to provide robust empirical evidence to inform ongoing public debates about cannabis regulation—debates that weigh hopes for reduced black‑market activity and safer consumption against concerns about normalization and potential increases in dependence or mental health harms.
Key findings
- Reduced problematic use: Participants with regulated, pharmacy-based access experienced a small but measurable decline in cannabis-related problematic consumption, especially among those who also used other illicit substances.
- Mental health unchanged or improved: No increase in depressive, anxiety or psychotic symptoms was observed with legal access; two-year follow-up suggests overall mental wellbeing improved for participants who remained in the study.
- Public health-oriented access may help: The results suggest that regulated access—combined with safer-use information and voluntary counseling—can reduce harms without worsening mental health outcomes.
Background and rationale
Proponents of regulated legal access argue it can undercut illegal supply, improve product safety, expand opportunities for counseling and education, and encourage lower-risk consumption. Critics worry that legal sales could normalize use, increase consumption rates, and lead to higher rates of addiction and mental health problems. The Weed Care study was designed to test these competing hypotheses using a randomized, controlled approach rather than observational data alone.
Study design
The trial enrolled 378 adult cannabis users between August 2022 and March 2023; 374 completed baseline assessments and were randomized. For the first six months participants were split into two groups: one group received public-health oriented access to regulated cannabis products sold in pharmacies (including safer‑use information and optional counseling), while the control group continued to obtain cannabis from the illegal market. Participants completed periodic questionnaires reporting their cannabis use and mental health symptoms. After six months the control group was offered access to the regulated program.
Main results
After six months, analyses showed a small reduction in cannabis misuse scores in the legal-access group compared with the control group. The reduction reached statistical support in some analyses and was most pronounced among participants who also used other drugs—an effect suggesting that regulated access and associated support measures may reduce harmful patterns of poly‑substance use. Importantly, there were no statistically significant increases in depression, anxiety or psychotic symptoms associated with legal access over the initial six‑month period. Two-year interim follow-up of roughly 300 continuing participants showed a general improvement in mental wellbeing, which study leaders interpret as evidence that legal access reduces some of the burdens associated with obtaining and using cannabis.
Interpretation
These findings indicate that public health‑oriented recreational cannabis access—delivered through regulated outlets with information and voluntary counseling—may lower cannabis-related harms without worsening short‑term mental health outcomes. The benefits were most evident among those using multiple substances, suggesting targeted regulatory and support measures could be particularly helpful in these subgroups.
About this research and credits
Author: Angelika Jacobs
Source: University of Basel
Contact: Angelika Jacobs – University of Basel
Image: Image credited to Neuroscience News
Original research (open access): Effects of legal access versus illegal market cannabis on use and mental health: A randomized controlled trial by Lavinia Baltes‑Flückiger et al., published in Addiction.
Abstract
Effects of legal access versus illegal market cannabis on use and mental health: A randomized controlled trial
Aims
The study measured the effects of public health‑oriented recreational cannabis access, compared with continued illegal-market sourcing, on cannabis use and related mental health outcomes in adult cannabis users.
Design
A two‑arm, parallel‑group, open‑label randomized controlled trial with follow‑up outcome measurement after six months.
Setting
The trial was carried out in Basel‑Stadt, Switzerland.
Participants
A total of 378 adults (aged 18 and older) were enrolled and randomized between August 2022 and March 2023; 374 participants completed baseline measures and were included in analyses.
Intervention and comparator
Participants were randomly assigned to regulated, pharmacy‑based recreational cannabis access with public health measures (regulated products, safer‑use advice, voluntary counseling, no advertising) or to a control group that continued obtaining cannabis via the illegal market.
Measurements
The primary outcome was self‑reported severity of cannabis misuse after six months, assessed with the Cannabis Use Disorders Identification Test – Revised (range 0–32). Secondary outcomes included depressive, anxiety, and psychotic symptoms, amount of cannabis consumed, and alcohol and other drug use.
Findings
Ten participants (2.7%) were not followed; primary analyses included those with complete data (182 vs. 182). The legal access group had a slightly lower mean cannabis misuse score (mean = 10.1) than the illegal market control group (mean = 10.9), with estimates supporting a small reduction in misuse. Subgroup analysis indicated reductions were concentrated among participants who used other drugs. No statistically significant changes were found across the predefined secondary mental health outcomes within the initial six‑month period.
Conclusions
Public health‑oriented recreational cannabis access may reduce cannabis use and related harms, particularly for people who use other drugs, without increasing short‑term mental health symptoms.