METH-abusing volunteers will undergo 6 sessions spaced 2-3 days apart. A single oral dose of prazosin (placebo, 1 mg, or 2 mg po) will be given in a randomized, double-blind design before METH or METH placebo administration in each session. METH will be given po in a dose (20 mg) that is well-tolerated by humans but that results in easily measurable effects by itself (Cruickshank and Dyer, 2009; Sevak et al, 2009; Parrot et al, 2011). Prior to and at several time points after prazosin/placebo,METH/placebo, or prazosin/METH administrations, self-report, cognitive performance and physiologic measures will be obtained.