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Article History

Received: 10 December 2025

Accepted: 1 July 2026

First Online: 29 July 2026

Declarations

Ethics approval and consent to participate: The study protocol received ethical approval from the independent Ethics Committee of UZ Brussels (reference 1432021000683). Written informed consent was obtained from all participants by the grassroots organisations before commencement of the interviews. The study was communicated to local and national legal authorities before the start of data collection, and each grassroots organisation had the necessary end-user licenses to preserve the heroin samples before transportation to the laboratory, which occurred two times a week.

Consent for publication: Not applicable. We provide the participants with the information that the study will only publish results on an aggregated level and that we will not publish individual data.

Competing interest: The authors declare no competing interest.