A comparative study found that methamphetamine and cocaine dependence were associated with larger differences in decision-making than in some other executive functions. Response inhibition did not show the same pattern. The result argues against using “executive impairment” as an undifferentiated label.
Van der Plas and colleagues compared 38 methamphetamine-dependent, 27 cocaine-dependent and 33 alcohol-dependent participants with 36 healthy comparison participants. The battery assessed Iowa Gambling Task decision-making, working memory, cognitive flexibility and response inhibition.
The study included men and women and examined sex-related patterns. It was an observational group comparison, not an experiment assigning people to develop dependence or administering a controlled intoxicating dose.
The cocaine and methamphetamine groups showed poorer complex decision-making, working memory and cognitive flexibility. The working-memory and flexibility differences were milder than the decision-making differences. Response inhibition did not show the same impairment pattern.
Decision-making differences were more pronounced in women than men within the cocaine and methamphetamine groups. This is a finding about the reported groups and tasks; it is not a rule about every woman or man with a substance-use history.
Age and education differed between clinical participants and controls. The investigators used covariance analyses, and most differences remained significant after adjustment. Nevertheless, adjustment for measured variables cannot exclude all preexisting vulnerabilities or unmeasured influences.
The study itself did not establish whether the cognitive differences preceded use, resulted from use, or reflected both processes. Drug-of-choice categories also cannot capture every exposure characteristic relevant to cognition.
One executive task cannot substitute for the others. A decision-making deficit does not prove a general inability to stop an action, and a nonsignificant inhibition result does not establish sound judgment in complex situations.
Forensic use requires identifying the function relevant to the event and independently assessing the individual. This battery supplies no concentration-based rule for intoxication or driving impairment.
Related reading: What a controlled driving study can establish.