Serum levels of methadone in maintenance clients who persist in illicit drug use.

This study examined pharmacological factors contributing to persisting drug abuse by methadone maintenance clients. Three groups of clients, drawn from one treatment programme, were studied: persistent heroin users, persistent benzodiazepine users, and control subjects who were not using illicit drugs in addition to methadone. Persistent abusers mostly had high trough serum methadone levels, and their ongoing drug use appears to reflect a preference for a different drug effect rather than inadequate methadone dose. Several clients did have the expectation that methadone should prevent them from using other drugs; such expectations may diminish the effectiveness of treatment.