Abstract
Social workers intervene with clients with co-occurring substance use and mental health disorders in their daily practice. Many social workers may not have a full understanding of the theories about why people have co-occurring disorders. The theory that social workers are most familiar with, the self-medication model, may not best explain the client's experience and may cause social workers to overlook the needs of some clients. In this article, the four main models used to explain why people have co-occurring disorders are examined, empirical literature related to each model is critiqued, and implications for practice, policy, and research are discussed.