This study will enroll individuals addicted to heroin who have completed a prior detoxification program at one of two addiction treatment hospitals in St. Petersburg, Russian Federation. Upon completing the detoxification program of 7-14 days, participants will have a period of inpatient rehabilitation. During this 3- to 4-week inpatient stabilization period, patients will be screened for study participation. Once stabilized, participants will begin the 6-month treatment phase of the study. During this phase, they will be randomly assigned to receive one of the following drug combinations on a daily basis: 50 mg of naltrexone and guanfacine placebo; 1.0 mg of guanfacine and naltrexone placebo; 50 mg of naltrexone and 1.0 mg of guanfacine; or naltrexone placebo and guanfacine placebo. All participants will have a designated family member who will be responsible for supervising medication compliance. Study visits will occur twice monthly. Participants will receive clinical management and medication compliance counseling at each visit; family members will also take part in the counseling sessions. Outcome measurements will include drug relapse, medication adherence, withdrawal symptoms, HIV risk factors, and psychiatric symptoms. Follow-up evaluations will occur 3 and 6 months following the end of treatment.