A randomized trial in Switzerland found that legal, regulated cannabis access may slightly reduce cannabis misuse compared to the illegal market, with benefits concentrated among people who also use other drugs.
Policy makers designing cannabis regulations, public health researchers, harm reduction advocates
First RCT comparing legal and illegal cannabis markets
What the researchers found
After 6 months, the legal cannabis group showed a trend toward lower cannabis misuse scores compared to the illegal market group (10.1 vs 10.9, p=0.052). Sub-group analysis revealed that the reduction was confined to legal access participants who also used other drugs. No significant changes were found for depression, anxiety, psychotic symptoms, or alcohol use.
Why it matters
This is the first randomized controlled trial directly comparing legal and illegal cannabis market effects on health outcomes. While observational studies of legalization exist, experimental evidence has been lacking.
The numbers in context
374 participants randomized. Cannabis misuse scores: 10.1 (legal) vs 10.9 (illegal), p=0.052. 97.3% follow-up rate. The benefit was concentrated among participants who also used other drugs (interaction p<0.001). No significant differences in secondary mental health outcomes.
How the study worked
Two-arm, parallel group, open-label randomized controlled trial in Basel, Switzerland. 374 adult cannabis users were randomized to receive legal cannabis through pharmacies (with safer use information and voluntary counseling) or to continue purchasing from the illegal market. Follow-up at 6 months.
What this study cannot tell us
Open-label design means participants knew their group assignment. Conducted in one Swiss city with specific cultural and legal context. Six-month follow-up may be too short to detect longer-term effects. The primary outcome narrowly missed statistical significance.
How to read the evidence
Strong: randomized controlled trial with 97.3% follow-up, though open-label design and borderline significance of primary outcome are limitations
When this study was published
Published in 2025 (Addiction) with data from 2022-2023
The bigger picture
This trial provides experimental evidence that regulated cannabis access, when combined with harm reduction measures, may reduce misuse. The finding that benefits concentrate among polysubstance users suggests that the regulated environment may be especially helpful for higher-risk individuals.
Questions still open
- Would a longer follow-up period reveal stronger effects? Why were benefits concentrated among polysubstance users? Would these results replicate in other countries?
Common questions
Did legal cannabis reduce harm?
Why is this study important?
Read the original research
Effects of legal access versus illegal market cannabis on use and mental health: A randomized controlled trial.
Addiction (Abingdon, England), 120(10), 1982-1992
Citation
Baltes-Flueckiger, Lavinia; Steinauer, Regine; Meyer, Maximilian; Guessoum, Adrian; Herrmann, Oliver; Mosandl, Christoph Felix; Kronschnabel, Jens; Pichler, Eva-Maria; Vogel, Marc; Walter, Marc. (2025). Effects of legal access versus illegal market cannabis on use and mental health: A randomized controlled trial.. Addiction (Abingdon, England), 120(10), 1982-1992. https://doi.org/10.1111/add.70080