Use of 'very low-dose phenobarbital' to investigate compliance in patients on reducing doses of methadone (detoxification).

Incorporation of very low doses of phenobarbital into a methadone linctus has enabled us to monitor the compliance of 7 patients receiving a reducing dose of methadone (detoxification) for treatment for opioid addiction. By measuring both plasma phenobarbital and methadone we detected 4 patients who consumed extra illicitly obtained methadone during the detoxification regime. Treatment outcome was poor; 11 of the original 18 patients dropped out of treatment within 14 days and of those who remained, 4 patients relapsed and reabused illicit drugs and 2 returned to a fixed dose of methadone. Laboratory measurements were successfully used to detect poor methadone compliance.