In this study, side effect complaints were compared between methadone patients on a stable dose with no heroin use for at least 3 months and matched non-drug-using controls; between methadone patients when using and not using heroin; and between patients in treatment (stable dosage, no heroin use for at least one month) and at follow-up, when not using any opiates and no longer in treatment. This last comparison was done for methadone, LAAM (l-alpha-acetylmethadol, methadyl acetate), and naltrexone patients. Methadone patients had more complaints than did non-drug-using controls; patients in methadone treatment felt worse when using heroin than when not using heroin; methadone, LAAM, and naltrexone patients felt worse while in treatment than when they left treatment and stopped using all opiates; the level of complaints for patients abstinent from opiates at follow-up was not different from that reported by non-drug-using controls. The difficulty of ascribing the symptom complaints to the drugs, in the absence of placebo-treated control groups, is discussed.