Subjects who successfully complete screening will report to the inpatient facility at an appropriate time the day before study drug administration to undergo pre-dosing study procedures (Day 1). The next morning (Day 1), all subjects will receive breakfast (approximately 6 hours before planned lofexidine dosing) and then ESRD subjects will begin their hemodialysis session. All subjects will receive a single, oral dose of 400 µg lofexidine HCl (two 200 µg tablets), dosed with 240 mL of water, the clock time for which will be approximately the same for both normal renal function subjects and ESRD subjects. Because ESRD subjects will be maintained on 3 times per week dialysis, lofexidine will be administered near the beginning of a 3-day between-dialysis interval.