Participants are required to have used MA by the smoked or IV route to avoid exposing participants to routes of administration that produce more intensive interoceptive effects. The age criteria were selected primarily to avoid enrolling participants with undiagnosed cardiovascular disease. Participants with active HIV disease are excluded to avoid potential exacerbation of their underlying disease; participants with asymptomatic HIV are included because this group is at high risk for MA dependence. Participants with asthma (or who take asthma medications) are excluded due to potential adverse interactions between beta agonist medications and MA.