Effects of Acute Doses of Prosocial Drugs Methamphetamine and Alcohol on Plasma Oxytocin Levels

Many drugs, including alcohol and stimulants, demonstrably increase sociability and verbal interaction and are recreationally consumed in social settings. One drug, 3,4-methylenedioxymethamphetamine (MDMA, ecstasy), seems to produce its prosocial effects by increasing plasma oxytocin levels, and the oxytocin system has been implicated in responses to several other drugs of abuse. Here, we sought to investigate the effects of 2 other social drugs on plasma oxytocin levels-methamphetamine and alcohol. Based on their shared capacity to enhance sociability, we hypothesized that both methamphetamine and alcohol would increase plasma oxytocin levels. In study 1, 11 healthy adult volunteers attended 3 sessions during which they received methamphetamine (10 mg or 20 mg) or placebo under double-blind conditions. Subjective drug effects, cardiovascular effects, and plasma oxytocin levels were measured at regular intervals throughout the sessions. In study 2, 8 healthy adult volunteers attended a single session during which they received 1 beverage containing placebo, and then a beverage containing alcohol (0.8 g/kg). Subjective effects, breath alcohol levels, and plasma oxytocin levels were measured at regular intervals. Both methamphetamine and alcohol produced their expected physiological and subjective effects, but neither of these drugs increased plasma oxytocin levels. The neurobiological mechanisms mediating the prosocial effects of drugs such as alcohol and methamphetamine remain to be identified.