Discussion
alcohol-use
ALCOHOL EFFECTS
Acute weighted oral doses of methamphetamine, when used alone or in combination with low doses of alcohol, produce prototypical physiological and subjective drug effects but do not reliably affect higher-order neurocognitive skills relative to alcohol-use alone. Sustained subjective stimulative effects and absence of additive performance deficits in the combined condition suggest at least some masking of biphasic alcohol effects over time, which may underlie motivations for co-consumption in recreational settings and increase propensity for harm.Even at low doses (mean BAC 0.029%), alcohol impaired performance in tasks of psychomotor speed and sustained attention, but not working memory. Impairment in these functional domains supports low-effect thresholds for alcohol intoxication starting from a very low BAC (Previous research has found that methamphetamine produced isolated improvement in psychomotor response speed during a working memory task and improved time-on-task performance proportionate to expected pharmacodynamic properties (Isolated impairment in the alcohol-only condition, relative to the combined methamphetamine and alcohol condition on measures of vigilance, and a general observation of preserved accuracy of performance without compromised speed of response may reflect ability of the psychostimulant to protect against gradual performance deterioration; however, these results were somewhat limited in scope. Nevertheless, the stimulant properties of methamphetamine were not altered by the biphasic effects of low doses of ethanol, and thus it is possible that there is at least some protective effect of methamphetamine against gradual performance degradation, even after lower doses of alcohol are consumed. The longevity of subjective effects and absence of clear sedation in the combined methamphetamine and alcohol condition, even beyond the expected half-life of alcohol and in contrast to known concentration curves, may increase the likelihood of repeated dosing (consuming more alcohol) for a longer duration. Indeed, methamphetamine pharmacokinetics were not altered by the concurrent administration of ethanol, which is consistent with previous acute dosing studies at similar doses (The small sample size is a notable limitation of the present study; however, the closely controlled design, coupled with multiple testing timepoints per experimental session for each treatment condition, ensures high data quality and expands a very limited research area. To date, only two studies have implemented a comparable combined methamphetamine and alcohol-dosing paradigm (Despite reductions in the global consumption of alcohol, rates of methamphetamine used continue to increase. Polydrug use represents an increasing concern for safety, and discerning potential interactive effects on performance and behaviour is critical for informing effective harm reduction strategies. Dissociation between these subjective effects and objective effects appears partially supported, whereby the stimulative effects of methamphetamine may mask some of the biphasic sedative properties of even low doses of alcohol. In practical terms, this may potentiate the reinforcing and hazardous effects of each drug and increasing the propensity for harm.