Issues: Completion of residential treatment for substance use disorder (SUD) relates to improvements in substance use and mental health. Findings from systematic reviews have been equivocal about which interventions work best for clients. There has been limited attention to the theories that explain the effectiveness of residential treatment.Approach: We conducted a realist review of the literature to identify program theories that would explain successful and unsuccessful outcomes from residential treatment for SUD. The unit of analysis was context-mechanism-outcome (CMO). Inclusion criteria were studies of residential treatment of more than 30 days for adults with SUD. Pharmacological studies were excluded.

Residential treatment of addiction remains a key element in addictions management, though high rates of attrition and relapse are reported, and underlying mechanisms of change remain unclear. This study aimed to complete the first stage of a realist evaluation—to develop an initial programme theory that would explain possible contexts and mechanisms of change leading to outcomes from a residential treatment programme for substance use disorders. Realist evaluation using key informant interviews and document review. Residential treatment centre in New Zealand. Four key informants (managers and caseworkers). Retroductive analysis (inductive and deductive) of semi-structured interviews and content analysis of documents. We identified one intermediate outcome of identity change that contributed to successful completion of residential treatment. The mechanisms leading to these outcomes were the development of a sense of belonging to the recovery community and a sense of hope and purpose. These mechanisms were activated in contexts including supportive and structured culture (staff and peers) and the absence of chaos. We developed an initial programme theory to explain successful completion of a residential treatment for SUD. Theories like this are important because practitioners can use them to increase the likelihood of replication of successful treatment. We found that realist evaluation provides researchers with appropriate philosophy and methods with which to explore and start to unravel some of the complexity within residential treatment for addictions.