Study to Evaluate the Exposures of Lofexidine and Its Major Metabolites in Subjects Seeking Buprenorphine Dose Reduction

Inclusion Criteria: * Have current dependency such that the subject is maintained on a daily dose between 8 and 24 mg of buprenorphine and is seeking reduction of their buprenorphine dose by at least 4 mg. * Urine toxicology screen positive for buprenorphine at Screening. * Agree to collection of blood samples for genotyping of CYP2D6 metabolizer status. * If female and of childbearing potential, subject must have been using birth control for at least 30 days and must agree to use an acceptable form of birth control through at least 30 days after the last dose of study drug. * If male, must agree to use an acceptable form of birth control throughout the entire study period and for 90 days after the last dose of study drug. Must not donate sperm for 90 days after the last dose of study drug. Exclusion Criteria: * Be a female subject who is pregnant or lactating. * Have a very serious medical illness not under control. * Have participated in an investigational drug study within the past 30 days. * Received any drugs that are known strong, moderate or weak inhibitors of cytochrome P450 (CYP) enzymes CYP1A2, CYP2C19, or CYP2D6, within 14 days or 5 half-lives (whichever is more) before Day -1. * Abnormal cardiovascular exam at Screening. * Subjects requiring the following will be excluded: Tricyclic antidepressants, which may reduce the efficacy of imidazoline derivatives; Beta-receptor blockers, to avoid the risk of excessive bradycardia.