People with longer methamphetamine abstinence showed less Stroop interference than recently abstinent participants in a pooled human study. The result suggests possible improvement in cognitive control, but does not prove that each individual recovers on a fixed timetable.
Salo and colleagues compared 38 recently abstinent participants, 27 abstinent for more than a year and 33 non-substance-abusing controls. Recently abstinent participants were approximately three weeks to six months into abstinence. The investigators pooled earlier behavioral data with newly collected data. This was a group comparison, not random assignment to abstinence or a longitudinal demonstration of change in the same people.
The results section reports greater reaction-time interference in recent abstinence than in controls or longer abstinence. Longer-abstinent participants did not differ significantly from controls on interference. These comparisons persisted after accounting for education and estimated reading ability. Error rates did not differ between the three groups. Thus a difference in interference-related speed should not be described as an increase in every type of task error.
Duration of use and abstinence were related to task performance, but the design cannot isolate recovery from differences between people who achieve longer abstinence and those assessed earlier. The source’s abstract and detailed results also differ in some statistical wording; conclusions should rely on the explicit group comparisons rather than inventing a precise universal recovery slope. Stroop testing measures a particular form of competing-response control. It does not directly establish driving safety, competence, truthful recall or an individual’s occupational ability. No blood or urine result in this report validates an abstinence-to-impairment clock. Case opinions require the person’s own history and functional assessment.
For a separate example of the limits of use-history comparisons, see our current-user driving study. The design and measured outcome determine which conclusions can be carried into an individual case.
Original investigation: doi:10.1016/j.jsat.2009.03.004.