Fourth, the substance abuse component of dual diagnoses among veterans is likely far more variable than is portrayed in the literature. The studies described in this review primarily address alcohol use while neglecting other prevalent substances of abuse. Certainly cannabis, cocaine, and opiates are common drugs of abuse but are typically lumped into a general “illicit drug use” category that fails to provide sufficient specificity. Drugs have different psychophysiological effects that may interact with specific psychiatric diagnoses to alter risk for adverse outcomes.