Participants in this double-blind study will be recruited among opioid dependent individuals already enrolled in a 6-day inpatient opioid detoxification program. Participants will be already receiving standard treatment to control discomfort during a methadone tapering schedule. Participants will be randomly assigned to one of three groups. Two of the groups will be given naltrexone; Group 1 will receive 0.125 mg each day, and Group 2 will receive 0.250 mg each day. Group 3 will receive a placebo. Participants will be evaluated upon enrollment for opiate addiction severity. They will continue to be evaluated daily for signs of withdrawal and salivary cortisol. An additional evaluation and urine test will be completed 1 day following discharge. Daily evaluations will take 15 minutes to complete. Seven days following discharge, participants will be contacted for a 20-minute phone interview. During the phone interview, participants will schedule an appointment to provide a final urine specimen for the detection of drugs of abuse.