Methamphetamine self-administration by humans

Rationale: Methamphetamine abuse has become increasingly problematic. Yet, the reinforcing effects of methamphetamine in humans have not been systemat ically evaluated. Objective: To characterize methamphetamine's reinforcing effects in human research participants under controlled laboratory conditio ns. Methods: Eight healthy research volunteers (one female, seven males) co mpleted this 20-day residential study. On days 1, 5, 9, 13 and 17, at 1000 hours, participants received the "sample" oral dose of methamphetamine (0, 5, 10 mg) that was available for the next 3 days and they also received an alternative reinforcer, a $1 voucher (redeemable for cash at study's end). Over a 3-day period, volunteers participated in an eight-trial choice proce dure, during which they had the opportunity to self-administer the dose of methamphetamine they most recently sampled or to receive the $1 voucher, Re sults: Participants' choice to self-administer methamphetamine significantl y increased when active methamphetamine (5 mg and 10 mg) was available comp ared to placebo. No difference of choice was noted between low-dose and hig h-dose methamphetamine. However, the sampled 10 mg methamphetamine dose sig nificantly increased several "positive" subjective ratings including "High, " "Good Drug Effect," and "Stimulated," whereas the sampled 5 mg methamphet amine dose did not. Both active methamphetamine doses caused significant re ductions in daily total caloric intake, relative to the respective placebo conditions. Conclusion: These data demonstrate that oral methamphetamine is a positive reinforcer in humans.