Brief Outline of the Study

This systematic review and meta-analysis examined the effectiveness of different substance use interventions for adults experiencing homelessness in high-income countries. The study compared abstinence-based interventions (which require participants to abstain from substance use) with harm reduction-based interventions (which seek to reduce harms without requiring abstinence) against treatment-as-usual. The review included 48 papers covering 34 unique studies and 15,255 participants, with studies primarily from the United States and Canada. The research aimed to understand which approaches work best to reduce problematic substance use among people experiencing homelessness.

Findings in Brief

• Interventions were more effective than treatment-as-usual in reducing substance use, with an overall effect size of -0.11 SD, though confidence intervals crossed zero indicating statistical uncertainty.
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• There was substantial heterogeneity across studies, with results sensitive to removal of lower quality studies.
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• Most papers (52%) were rated as low confidence, primarily due to high participant attrition rates that fell below acceptable standards.
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• Abstinence-based interventions showed an average effect of -0.28 SD compared to treatment-as-usual, while harm reduction interventions showed minimal effect at 0.03 SD.
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• Contingency Management (providing vouchers for abstinence) was highly effective with an average effect of -0.47 SD.
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• Assertive Community Treatment (ACT) and Intensive Case Management (ICM) showed no significant improvement over treatment-as-usual for substance use outcomes.
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• Group Work, Harm Reduction Psychotherapy, and Therapeutic Communities showed promise for reducing substance use.
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• Motivational Interviewing and Talking Therapies (including CBT) showed mixed results.
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• Residential Rehabilitation was no better than treatment-as-usual.
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• Only three papers focused specifically on women experiencing homelessness, with three-quarters of all participants being men.
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• The evidence base lacks robust UK-specific studies, with no included studies from the United Kingdom.

Recommendations in Brief

• Contingency Management interventions should be prioritized as they demonstrate strong evidence of effectiveness in reducing substance use.
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• Future research should focus on developing UK-specific evidence, as current findings are primarily from North America with different policy and service contexts.
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• More research is needed on interventions specifically designed for women experiencing homelessness and problematic substance use.
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• Studies should improve methodological quality, particularly around participant retention and attrition management.
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• The debate between abstinence-based versus harm reduction approaches may be less important than focusing on specific interventions that demonstrate effectiveness.
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• Individual interventions should be evaluated based on their specific components and delivery methods rather than broad categorization as abstinence or harm reduction-based.
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• Future evaluations should include longer follow-up periods and more robust outcome measures to better understand sustained effectiveness

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