Background: Assertive Community Treatment (ACT) has been studied extensively in people with severe mental illness, but there have only been a few clinical trials in which substance use was one of the measured outcomes.

Objective: The goal of this article was to describe the efficacy of ACT in treating co-occurring substance use disorders and suggest approaches to make it more efficacious.

Design: A literature review was conducted and randomized clinical trials describing ACT's impact on substance use were reviewed.

Results: Four randomized clinical trials of ACT that measured substance abuse adequately were identified, all of which showed small to no effect on substance abuse compared with control conditions. Methodological issues might account for the small effects. ACT might further reduce substance use by being paired with evidenced-based substance abuse treatment, helping clients become housed or helping them manage their money better.

Conclusion: Integrated ACT, in which the ACT team provides substance abuse counseling, has the potential to reduce substance use by several mechanisms, but this has been difficult to demonstrate in clinical trials when participants in control groups receive similar interventions.