Subjects who successfully complete screening will report to the inpatient facility at an appropriate time the evening before study drug administration (Day 1) to ensure a minimum 10 hour fast. The next morning (Day 1) while still fasting, subjects will receive a single, oral dose of 400 µg lofexidine HCl (two 200 µg tablets). Blood samples will be collected for pharmacokinetic (PK) analysis at multiple time points over the next 144 hours (Day 7). Pooled urine samples will be collected at 0 3 hours, 3 6 hours, 6 12 hours, 12 24 hours, 24 48 hours, 48 96 hours, 96 120 hours and 120 144 hours post-dose. Safety will be assessed by recording adverse events (AEs), measuring vital signs (blood pressure and pulse rate) and clinical laboratory tests (chemistry, hematology, and urinalysis), recording 12 lead safety and Holter electrocardiograms (ECGs), and performing physical exams.