Substance use among the mentally ill: prevalence, reasons for use, and effects on illness.

Substance use among a random sample of mentally ill, community-based patients was examined. Current use was found to have declined substantially from a high lifetime prevalence, and a family history of substance abuse was associated with moderate to heavy use. No association was found between heavy substance use and elevated psychopathology, hospitalization, or medication noncompliance. Hospital admissions and some symptoms were less prevalent among users preferring marijuana.