Background: In France, addiction care in prison usually consists of nurses’ interventions, medical care and socio-educational programs, but new alternatives have arisen, namely the therapeutic community (TC) model. This pilot study aims to evaluate the effectiveness of this prison-based TC in comparison with classic and socio-educational care offered in French prisons. Methods: To compare these three types of prison-based care, two detention centers’ files were screened for use of multiple drugs, willingness to participate and absence of psychiatric comorbidities incompatible with group therapy. A custom questionnaire was built based on the fifth version of the Addiction Severity Index. It investigates medical status, employment and support, primary addiction status, legal status, social/familial status and psychiatric status through various items. Results: Our sample only consisted of male repeat offenders with a mean age of 37.7 ± (9.1) years. Primary addiction status improvement was observed for all care studied but was more important in TC than in classic care. Self-esteem and social/familial status saw significant improvement throughout TC care. Conclusions: The TC model represents an alternative to classic and socio-educational care in French prisons. More studies are needed to assess the extent of the benefits provided on both the medical side and economic side.