Stress is one of the more common reasons cited by addicts for continual drug use and relapse. Naltrexone treatment of opiate addicts suffers from high rates of drop-out and relapse. This may be a result of naltrexone's inability to reduce symptoms of stress during early recovery. Treatment approaches that target both drug-induced and stress-induced relapse may prove to be more beneficial than targeting drug-induced relapse alone. Lofexidine is a drug that reduces the physical symptoms of opiate withdrawal and may prove to have stress-reducing capabilities. The purpose of this study is to determine the maximal safe dose of lofexidine tolerated in naltrexone-treated opiate addicts and to find an optimal lofexidine induction schedule. The study will also assess any side effects that occur during a discontinuation phase of lofexidine.