Methamphetamine increased willingness to choose a more demanding laboratory task, but those changes were not correlated with drug-induced euphoria or liking in a controlled study of healthy adults. Feeling better and choosing greater effort were separate measured outcomes.
A single dose and a specific decision task
Hahn and colleagues compared 20 mg oral methamphetamine with placebo in a double-blind, within-subject design. Participants attended an orientation session and two four-hour drug sessions separated by at least three days. Behavioral tasks began one hour after the capsule.
The Effort Expenditure for Rewards Task offered a choice between an easier option and a harder option. The easy task required 30 key presses with the right index finger in seven seconds for a possible $1 reward. The hard task required 100 presses with the left little finger in 21 seconds for possible rewards from $1.24 to $4.21. Reward probabilities were 12%, 50% or 88%, disclosed before the choice.
The endpoint was how frequently participants selected the harder task. It was not an examination score, work productivity measurement or test of driving skill. Choosing more effort is not automatically the best decision in every setting.
Why the denominators differ
Of 113 participants who completed the study, 96 remained in the behavioral analysis after exclusions for missing data, invariant hard/easy choices or sessions containing only timeouts. The final behavioral sample included 48 men and 48 women.
Five additional participants were excluded from computational modeling because their choices were better described by a bias model, leaving 91. Subjective analyses had 94 participants for euphoria and 92 for drug liking. These are analysis-specific samples; they are not four independent experiments or a single sample of 113 with complete observations.
Baseline effort changed the size of the response
Investigators divided participants into two groups of 48 using orientation-session task performance. Methamphetamine increased overall hard-task selection in both baseline groups, with a larger increase in the low-effort group. Reported within-group standardized effects were d = 0.76 for the low-baseline group and d = 0.42 for the high-baseline group.
The higher-baseline group therefore should not be described as showing no behavioral response. The more selective null finding concerned a computational parameter, not the overall frequency of hard choices.
What the computational model added
The model estimated sensitivity to effort cost, reward probability and consistency of choice. Methamphetamine reduced the estimated effort-cost parameter in the low-baseline group, but the corresponding comparison in the high-baseline group was nonsignificant. The drug did not significantly alter the probability-sensitivity parameter.
These are model-derived quantities fitted to choices. They are not direct measurements of dopamine, physical stamina or a person’s real-world motivation. The authors did not measure dopamine function, and proposed neurotransmitter explanations remain hypotheses.
Effort changes did not track euphoria
| Outcome pair | Reported correlation | Interpretation |
|---|---|---|
| Drug-associated hard-choice change and euphoria change | r = 0.007; p = 0.948 | No significant relationship detected |
| Drug-associated hard-choice change and drug-liking change | r = −0.031; p = 0.768 | No significant relationship detected |
The drug increased euphoria and liking at the group level, yet people with larger subjective changes did not reliably show larger effort changes. A group effect on two measures does not imply that the two changes correlate across individuals.
Conversely, nonsignificant correlations do not prove that mood and motivation can never interact. They define the relationship observed with these measures, participants and experimental conditions.
Limits on claims about enhancement or impairment
The sample consisted of selected healthy adults aged 18–35, free of major psychiatric conditions. One dose was tested. A median split creates study-specific categories, rather than identifying a clinical disorder or a stable diagnosis of low motivation.
The experiment provides no blood-concentration cutoff, validated impairment classification or basis for deciding whether an individual drove safely. It also does not establish efficacy for depression or ADHD. The narrow finding is a change in laboratory effort-based choices that was larger in lower baseline performers and did not correspond to the measured subjective drug effects.
Primary scientific source
Hahn EC, Molla H, Cooper JA, DeBrosse J, de Wit H. Effects of methamphetamine on human effort task performance are unrelated to its subjective effects. Psychopharmacology. 2026;243:199–209; first published online July 8, 2025. doi:10.1007/s00213-025-06853-4. Original commentary on the supplied controlled human study; publication year follows the issue citation.
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