Regulated Cannabis Access May Reduce Problematic Use

In an effort to provide an evidence base for cannabis policy reform, researchers in Switzerland have begun assessing the effects of regulated cannabis access. The Weed Care study, launched in January 2023, is a collaboration between the Department of Health of the Canton of Basel-Stadt, the University of Basel, the University Psychiatric Clinics Basel and Psychiatric Services Aargau.

This study is the first randomized controlled trial in Switzerland designed to directly compare the impacts of legal versus illegal cannabis procurement on user behavior and mental health.

Study design and participant structure

For the first 6 months of the study, approximately 370 adult cannabis users were assigned to one of two groups. Half were given legal access to cannabis products through nine local pharmacies and were offered optional counseling. The control group continued to obtain cannabis from the illegal market.

Both groups provided data on their cannabis use and psychological health through periodic questionnaires. The study aimed to assess not only patterns of consumption but also the psychological effects commonly linked to cannabis use, such as anxiety and depression.

“There has never been a controlled, randomized study like this before,” said Dr. Lavinia Baltes-Flückiger.

Effects on consumption and mental health

Findings from the first phase, published in Addiction, indicate that problematic cannabis use declined modestly among participants with legal access.

Problematic use was defined as use associated with negative health, psychological or social consequences, even in the absence of clinical dependence.

The most notable reduction in problematic use was seen among individuals who used cannabis alongside other drugs.

“In this subgroup, problematic cannabis use experienced a significant drop,” says Baltes-Flückiger.

No significant differences were observed between the two groups in terms of depression or anxiety symptoms after the six-month period.

Following this initial phase, individuals in the control group were also granted access to legally distributed cannabis, as was agreed upon at the start of the trial.

Continuing outcomes

An interim analysis conducted after two years of study suggests ongoing mental health improvements in participants who have remained involved. The team reports a general easing of psychological strain among these individuals, with continued legal access appearing to play a supportive role.

Further long-term analysis is expected to offer deeper insights into how structured access to regulated cannabis may influence behavior and health over time.

Reference: Baltes‐Flueckiger L, Steinauer R, Meyer M, et al. Effects of legal access versus illegal market cannabis on use and mental health: A randomized controlled trial. Addiction. 2025:add.70080. doi: 10.1111/add.70080

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