Effects of receiving additional off-site services on abstinence from illicit drug use among men on methadone: a longitudinal study.

Health and psychosocial service needs that may be co-morbid with opioid addiction may impede the success of drug treatment among patients attending methadone maintenance treatment programs (MMTPs). This longitudinal panel study investigates whether receipt of services from one or more helping professionals outside of the MMTP confers a benefit for drug treatment outcomes among a random sample of male MMTP patients (N=356). Each participant was interviewed 3 times, with 6 months between each interview. Since this observational study did not employ random assignment, propensity score matching was employed to strengthen causal validity of effect estimates. Results support hypotheses that receiving additional off-site services has significant beneficial effects in increasing the likelihood of abstaining from cocaine, heroin, and any illicit drug use over both the ensuing 6- and 12-month time periods. These findings indicate that receipt of additional medical and/or psychosocial services enhances the efficacy of methadone treatment in increasing abstinence from illicit drug use.