The purpose of this article is to examine how addiction treatment is organized in prisons and how it has evolved, as well as how the prison environment tends to concentrate a high proportion of drug users and may encourage drug use and risky behaviors. Method: The analyses were conducted by cross-referencing various data sources: a review of the literature, existing quantitative data, and qualitative data from focus groups and working groups. Results: The analyses show that the management of alcohol-related issues in prison has improved thanks to the professionalization of staff. The availability of opioid substitution therapy is now adequate, and its continuity upon entry into and release from prison appears to be ensured in most cases. Nevertheless, prison also contributes to the intensification and/or initiation of substance use, due to the illegal circulation of products or medications, and the risk of infection appears to be high. Conclusion: Based on the analyses, it appears necessary to improve prevention and health education in prisons, to integrate social and health care services, to adapt and diversify addiction treatment, and to improve the collection of epidemiological data on the health of inmates. [author’s abstract]