1 July 2025

Weed Care study extended

Lower-risk consumption methods and drug checking aim to encourage more conscious cannabis use.

Following a positive interim assessment, the Canton of Basel-Stadt is extending the “Weed Care” project by 18 months until January 2027. This randomized controlled intervention study, followed by an observation phase, investigates the effects of regulated cannabis sales through pharmacies in Basel-Stadt on consumption behaviour and health. The study extension incorporates participant feedback from the first phase (January 2023 to July 2025) and integrates key findings into the revised study design.


Harm Reduction and Consumption Control

The current product range – four cannabis flower products and two hashish products – will be expanded to include two e-liquids and two tinctures. These non-inhalative forms of administration address both the health risks of smoking and participants’ interest in alternative delivery methods.

Interim results from Weed Care also show that around half of the participants continue to obtain cannabis from the black market despite legal access. As a response, a voluntary drug checking service will be introduced during the study extension. Participants can have illegally purchased cannabis tested for THC content and potential contaminants – an initiative aimed at fostering consumption awareness and product quality consciousness.


Cross-Over Design to Evaluate Black Market Influence

In addition, a cross-over comparison will be conducted between the two groups from the initial study phase and those in the extension. By switching participants between the intervention and control conditions after a set period, researchers can more precisely assess how renewed access to the illegal market affects consumption patterns and mental health.

Study design of the Weed Care study and its extension
(Source: weedcare-basel.ch)

The Outpatient Study Center remains the central point of contact

Of the original 378 participants, 277 will also take part in the extended study phase. The on-site management team from the Department of Clinical Research will continue to serve as the primary point of contact for study participants and the participating pharmacies. In addition to administrative tasks and coordination, the team is responsible for documenting serious adverse events (SAEs) and maintains close contact with the study physicians. The selected pharmacies will remain part of the decentralized supply structure as before.


Scientific Evidence for Regulatory Policy

The scientific findings from Weed Care – supplemented by results from other pilot projects in Switzerland – aim to provide an evidence-based foundation for discussions about a forward-looking and responsible cannabis policy. The focus is on prevention, quality assurance, and the reduction of the illegal market.