Risk and protective factors for relapse after residential substance use treatment: a systematic review and meta-analysis

BACKGROUND: Relapse after residential treatment for substance use disorder (SUD) remains common, yet no prior systematic review and meta-analysis has comprehensively synthesized the risk and protective factors associated with post-discharge relapse. We aimed to identify and quantify factors associated with relapse after residential SUD treatment, while also examining whether outcomes differed by primary substance and by treatment type (mandatory versus voluntary). METHODS: We conducted a PRISMA 2020 systematic review and meta-analysis registered with PROSPERO (CRD420251252324). PubMed, Embase, Scopus, PsycINFO, Web of Science, CINAHL Plus and grey literature were searched from inception to March 31, 2026. Primary studies of residential, inpatient, or therapeutic community SUD treatment reporting relapse-related outcomes were included. Random-effects inverse-variance models were used to pool risk ratios (RRs) for binary outcomes and standardized mean differences (SMDs) for continuous outcomes. Methodological quality was assessed using the NIH Quality Assessment Tool and RoB-1 for observational studies. RESULTS: Sixty-one studies involving 18,693 participants were included: 60 cohort studies and one cross-sectional study. Twenty-seven studies were rated Good and 34 Fair. Interventions modestly increased abstinence (RR, 1.13; 95% CI, 1.03-1.25). Relapsed participants had higher depression scores (SMD, 1.45; 95% CI, 1.23-1.66), whereas psychological distress was lower among abstinent participants, and self-efficacy was higher among abstinent participants after harmonizing the direction of effects. Longer treatment duration was associated with better outcomes, although heterogeneity was extreme and the pooled magnitude should be interpreted cautiously. Peer-support-specific analysis showed improved abstinence, whereas broader continuing-care or intervention analyses produced a separate estimate. Alcohol was the dominant substance category, followed by polysubstance, opioids/heroin, cocaine, and methamphetamine use. Descriptive evidence suggested lower 6- to 12-month abstinence in heroin-focused than alcohol-focused cohorts, but no study compared substances within one framework. Two studies examined correctional or prison-based mandatory settings, and none compared mandatory with voluntary treatment. CONCLUSIONS: Relapse after residential SUD treatment was associated with greater depressive burden and lower self-efficacy, whereas peer support, longer treatment duration, and adherence-related interventions were associated with better outcomes. Evidence was insufficient to draw firm conclusions regarding substance-specific differences or mandatory versus voluntary treatment effects, underscoring the need for better-designed comparative studies that standardize relapse definitions, classify treatment voluntariness, and report outcomes by primary substance category. CLINICAL TRIAL NUMBER: Not applicable.