The A‑BRAIN project, funded under the NEURON Joint Call (grant 01GP1823) and carried out by the Leibniz Institute for Prevention Research and Epidemiology (BIPS) from 1 April 2018 to 31 May 2022, investigated how the brain‑disease model of addiction (BDMA) is perceived by key stakeholder groups. The study’s central aim was to map the dissemination and implications of a neuroscience‑based understanding of addiction across international research communities and legal‑forensic systems in Germany, the United States, Finland, and Canada.

A rapid review of the literature guided the development of a questionnaire for researchers, which was subsequently adapted for representatives of legal and forensic institutions. Data were collected through online surveys administered with LimeSurvey, and participants were recruited directly or via professional associations. The German legal cohort comprised 1,000 respondents, of whom 35.5 % were lawyers, 19.4 % psychologists or psychiatrists, 11.3 % law enforcement officers, 6.5 % business and finance professionals, 17.7 % other roles, and 9.7 % undecided. Gender distribution was 43.1 % male and 56.9 % female, with 2.7 % unknown. Current professional roles were 46.4 % lawyers, 19.6 % judges, 3.6 % public prosecutors, 14.3 % forensic medical staff, 1.8 % forensic psychologists or psychiatrists, 12.5 % researchers, and 1.8 % other.

Among researchers, approximately 60 % endorsed brain‑based explanations of addiction and considered them evidence‑based. Nearly 80 % found such explanations helpful for understanding addiction, yet more than 60 % viewed the BDMA as an overly simplistic reduction of a complex phenomenon. In contrast, U.S. criminal‑law students rated neuroscience explanations as both important and widespread, and they were more likely to see them as integral to legal practice. German legal participants acknowledged the potential relevance of neuroscience in their professional context but reported that it currently plays a minor role within the German system. Both German and U.S. groups assessed the responsibility of individuals with addiction similarly, with a clear majority holding addicts accountable for their actions regardless of any medical basis for their condition.

The project’s sub‑studies—A through D—focused respectively on international researchers, U.S. and German legal stakeholders, Finnish stakeholders, and Canadian stakeholders. Each sub‑study employed a mixed‑methods approach, combining quantitative survey data with qualitative interviews to capture nuanced perspectives. The findings collectively illustrate a divergence between scientific endorsement of the BDMA and its limited penetration into legal frameworks, especially in Germany. They also highlight a shared belief in the importance of accountability for addictive behavior across jurisdictions.

Collaboration was central to the project’s design and execution. The Leibniz Institute coordinated the research, while partners from universities and professional bodies in the United States, Finland, and Canada contributed expertise and facilitated access to their respective stakeholder communities. The project’s timeline spanned four years, during which data collection, analysis, and dissemination activities were systematically planned and executed. Results were shared through peer‑reviewed journal articles, conference presentations, and policy briefs, ensuring that both scientific and legal audiences could engage with the evidence. The A‑BRAIN initiative thus provided a comprehensive, empirically grounded assessment of how a brain‑based model of addiction is understood and applied across diverse professional landscapes.