A controlled study found that a single dose of modafinil improved sustained attention across participants, while most other cognitive comparisons were nonsignificant. It supports a limited, task-specific effect rather than a general restoration of cognition in methamphetamine dependence.
The study included 24 methamphetamine-dependent participants and 17 healthy participants. In a randomized, double-blind crossover design, participants received a single oral 200-mg dose of modafinil and placebo on separate occasions. Tests examined inhibitory control, working memory, processing speed and attention.
Modafinil was the experimental medication. The study did not administer methamphetamine as a performance enhancer and did not determine the effect of a methamphetamine blood concentration on driving.
Across participants, modafinil improved sustained attention. No significant improvement was found on the other cognitive tests in the overall analysis. Within the methamphetamine-dependent group, participants reporting more frequent baseline use showed a greater modafinil effect on inhibitory-control and processing-speed measures than less frequent users.
The subgroup result should remain attached to its subgroup. It does not mean that every dependent participant improved, nor that frequent use is a validated rule for prescribing the medication. A task-specific benefit also cannot establish abstinence or successful treatment.
Only one dose was tested acutely. The experiment therefore cannot establish a dose-response curve or the effects of sustained treatment. Some cognitive measures occurred after the anticipated peak-concentration period, and testing-session intervals differed between groups. Baseline cognitive performance beyond estimated intelligence was not independently measured before treatment conditions.
The investigators also discussed education and intelligence as important influences on group comparisons. A nonsignificant difference between clinical and control participants should not be treated as proof that their cognitive profiles are identical.
This is preliminary evidence that an intervention can affect one cognitive function without improving all functions tested. It addresses a different question from experiments administering methamphetamine itself. Neither type of laboratory result establishes that an individual is safe to drive.