Stopping Criteria Participants must continue to meet inclusion criteria in order to remain in the protocol. Thus, MA administration procedures will not be initiated if there are clinically significant arrhythmias or if vital signs are outside of acceptable ranges: Resting Pulse: 50-90 beats per minute. Systolic Blood Pressure: 105-140 mm Hg Diastolic Blood Pressure: 45-90 mm Hg In addition, repeated doses of MA will not be administered (and the study physician or nurse practitioner will halt continued MA delivery) if there are behavioral manifestations of MA toxicity (agitation, psychosis, inability to cooperate with study procedures). Note that participants remain eligible to remain in the study provided that vital signs do not exceed the limits below.