A pioneering Swiss study has found that legal access to cannabis leads to a reduction in problematic consumption, particularly among individuals who use cannabis alongside other drugs. Conducted in Basel, the Weed Care project offers the first randomized, controlled comparison in Europe between legal and illegal cannabis procurement — with implications that may shape future drug policy far beyond Swiss borders.
First-of-its-Kind Study Offers Direct Comparison
The Weed Care study began in January 2023 as a collaboration between the University of Basel, the University Psychiatric Clinics Basel (UPK), Psychiatric Services Aargau, and the Addiction Department of the Department of Health of the Canton of Basel-Stadt. Approximately 370 participants were randomly divided into two groups: one was given access to legally regulated cannabis through one of nine designated pharmacies and offered optional counseling; the other continued to purchase cannabis on the black market.
Participants filled out regular surveys about their cannabis use and mental well-being. After six months, researchers observed that those with legal access reported lower levels of problematic consumption — defined not only as dependency but as use that negatively affects physical health, mental stability, or social functioning.
Clear Benefits for Polydrug Users
The decline was especially marked among those who used other substances in addition to cannabis. In this subgroup, legal access was associated with a statistically significant reduction in harmful patterns of use.
“We saw a clear drop in problematic cannabis consumption among polydrug users who had access to regulated products,” said Dr. Lavinia Baltes-Flueckiger, lead author of the study and deputy head of Psychiatric Services Aargau.
The study’s findings, recently published in the journal Addiction, suggest that legal cannabis sales, when coupled with education and access to safer products, can play a constructive role in harm reduction — rather than exacerbating addiction risks, as critics of legalization often claim.
No Increase in Mental Health Issues
One of the most debated fears around cannabis legalization is the potential increase in mental health disorders. However, the Swiss team found no difference between the two groups in terms of depression, anxiety, or other psychiatric symptoms after six months.
“This is an important reassurance,” said Professor Marc Walter, head of the study and director at Psychiatric Services Aargau. “Legal access appears to support mental health rather than undermine it.”
After the initial six-month period, participants in the control group were also given legal access to cannabis — an arrangement made clear from the start to encourage participation. Two years into the study, around 300 participants remain actively involved, with ongoing assessments showing an overall improvement in mental well-being.
Legal Access Reduces Pressure on Consumers
For those studying the intersection of policy, public health, and personal behavior, the early data from Weed Care suggest that legalization doesn’t simply offer a new point of sale — it changes the entire context of cannabis use.
“Legal supply takes pressure off users,” Walter explained. “It’s not just about convenience — it’s about safety, transparency, and access to professional guidance.”
The study is ongoing, with further findings expected to inform Switzerland’s national debate on cannabis policy. As more countries consider shifting toward regulated cannabis markets, Basel’s data-driven approach may serve as a model for others exploring harm-reduction strategies.
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