Why Men and Women Responded Differently on a Methamphetamine Reaction-Time Task

In a controlled experiment, methamphetamine shortened reaction times in women but did not significantly shorten them in men. The result was not a general demonstration that the drug improved reward-based decision-making.

The experiment and its participants

Mayo and colleagues analyzed task data from 44 men and 29 women. Participants attended four double-blind sessions, receiving methamphetamine or placebo twice each. The monetary incentive delay task used cues for potential monetary gains, losses and no incentive. Subjective and cardiovascular measures were assessed separately.

Faster responding was not selective for reward

Participants generally responded faster to larger incentives. Methamphetamine’s reaction-time effect in women occurred across cue types, rather than specifically strengthening responses to rewards. The reported drug-by-gender interaction was significant, while the overall drug term alone was not. These are different statistical questions.

Baseline differences complicate a simple explanation

Men responded faster under placebo, raising the possibility that baseline speed affected room for improvement. The researchers considered that explanation, while noting that incentives could still elicit faster responses. Greater reported vigor and less sedation in women also should not be confused with a complete assessment of cognition.

Limits for an individual opinion

This was human drug-administration research in healthy, nondependent volunteers. It was not an observation of intoxicated drivers, and it did not establish sex-specific blood or oral-fluid impairment cutoffs. A group interaction cannot predict every woman’s or man’s response. Task design, baseline ability and the sampled population must remain attached to the finding; faster button presses alone do not demonstrate safe driving.

Related evidence

For a different perspective on interpreting stimulant evidence, see our analysis of controlled human performance findings. Its study population and outcome should remain separate from the present findings.

Primary research

Gender differences in the behavioral and subjective effects of methamphetamine in healthy humans. Original human research. doi:10.1007/s00213-019-05276-2.