Acute and residual interactive effects of repeated administrations of oral methamphetamine and alcohol in humans

Although methamphetamine and alcohol are commonly used together in a binge-like pattern, there is a dearth of empirical data investigating the repeated effects of this drug combination. The current study examined acute and residual mood, performance, and physiological effects of methamphetamine alone, alcohol alone, and the combination. Nine adult male volunteers completed this 20-day within-participant, residential laboratory study. During four 5-day blocks of sessions, participants were administered oral methamphetamine (0, 10 mg) combined with alcohol (0, 0.375, 0.75 g/kg) three times (day 2: AM, day 2: PM, and day 3: PM). Breath alcohol concentrations, cardiovascular, subjective, and cognitive/psychomotor performance effects were assessed before drug administration and repeatedly thereafter. Subjective and objective sleep measures were also assessed; residual effects were assessed on days 3–5 of each block. Following the first drug administration, the methamphetamine–alcohol combination produced greater elevations of heart rate and ratings of “good drug effect” compared to either drug alone. Methamphetamine attenuated alcohol-related performance decrements and feelings of intoxication, whereas alcohol attenuated methamphetamine-related sleep disruptions. By the third administration, many of these effects were significantly diminished, suggesting that participants developed tolerance. Few residual effects were observed. These data show that methamphetamine combined with alcohol produced a profile of effects that was different from the effects of either drug alone. The largely positive effects of the drug combination (i.e., greater euphoria, and fewer performance and sleep disruptions) might explain why these drugs are often used in combination.