Basel, Switzerland became the first European city to launch a regulated adult-use cannabis commerce pilot trial in January 2023. Known as Weed Care, the study allows registered participants to purchase lab-tested, quality-controlled cannabis from authorized pharmacies instead of the illegal market. After more than three years of operation, authorities say the results are overwhelmingly positive.
The pilot trial is a collaboration between the Department of Health of the Canton of Basel-Stadt, the University of Basel, the University Psychiatric Clinics Basel (UPK), and Psychiatric Services Aargau. Around 300 participants remain active in the study, which is structured as a two-arm, parallel group, open-label, randomized controlled trial, the first of its kind anywhere in the world.
Products sold through the program must meet strict quality standards. All cannabis is free of pesticides, impurities, and synthetic cannabinoids, with active ingredient content clearly declared on the packaging. The goal is to determine whether regulated access through pharmacies produces better health outcomes than the current situation of illegal acquisition.
Consumption Did Not Increase
One of the most significant findings is that cannabis consumption among participants did not rise. This directly contradicts a core argument used by opponents of cannabis reform across Europe, who claim that legal access inevitably leads to higher rates of use.
The Canton of Basel-Stadt's health department reported that the introduction of non-smoked cannabis products last autumn, including vaporizers and oils, has been successful. These alternative consumption methods now account for nearly one fifth of all use within the program, yet total consumption has remained stable. The shift away from smoking represents a meaningful reduction in health risks.
Tobacco-mixed joint smoking, which has long been the dominant method of cannabis consumption in Europe, dropped significantly among participants. This is a particularly important outcome given that the health risks of cannabis use are closely tied to the inhalation of combustion byproducts and tobacco.
Mental Health Outcomes Improved
In May 2025, an interdisciplinary research team published the first academic findings from the Weed Care trial in the peer-reviewed journal Addiction. The study measured the effects of regulated cannabis access compared with the illegal market on cannabis use and related mental health outcomes after six months.
Researchers used the Cannabis Use Disorders Identification Test (Revised) to measure severity of cannabis misuse, alongside assessments of depressive, anxiety, and psychotic symptoms, consumption amounts, alcohol use, and other drug use. The findings showed that regulated access may decrease cannabis use and cannabis-related harms, especially among those who also use other substances.
The University of Basel reported that the study was able to dispel fears that legalization could worsen psychopathological symptoms associated with cannabis use. After the first six months, there was no difference between the regulated-access group and the control group in terms of depression, anxiety, or other symptoms. An interim assessment after two years showed a significant improvement in mental health among active participants.
A Landmark for Evidence-Based Policy
The significance of the Weed Care study extends far beyond Switzerland. As Europe's first randomized controlled trial of regulated cannabis sales, it provides a level of scientific rigor that policy debates have historically lacked. Previous evaluations of cannabis legalization have relied on observational data from jurisdictions like Canada, Uruguay, and US states, which are useful but cannot control for confounding variables the way a randomized trial can.
The results arrive at a critical moment for European cannabis policy. The Netherlands is evaluating whether to expand its wietexperiment, which currently operates in 10 municipalities. Germany is refining its adult-use framework after legalizing cannabis clubs and home cultivation in 2024. Czechia legalized home cultivation in January 2026 and is developing a commercial market. In all of these countries, opponents continue to argue that regulated access will increase use and harm mental health.
Basel's data suggests otherwise. Three years of evidence from a rigorous, controlled trial indicates that regulated, quality-controlled access through pharmacies reduces health risks without driving up consumption. For policymakers weighing the next steps on cannabis reform, the Weed Care study may be the strongest evidence yet that regulation works.
