Executive functioning is an umbrella description, not a single measurable ability. A 2009 comparison of alcohol-, cocaine- and methamphetamine-dependent adults found different patterns across decision-making, working memory, switching and response inhibition. Its null results limit a claim of uniformly impaired executive control.
The four participant groups
Van der Plas and colleagues enrolled 33 alcohol-dependent participants, 27 cocaine-dependent participants, 38 methamphetamine-dependent participants and 36 healthy comparison participants: 134 people overall. The methamphetamine group included 25 women; the other groups also included both men and women.
Substance-dependent participants were tested near discharge from treatment after at least 15 days of abstinence. Urine screening and breath alcohol testing were performed before assessment. This was an observational comparison of existing groups, not a controlled administration study. Primary drug-of-choice categories do not mean that each group had an exclusive lifetime exposure to one substance.
Decision-making differed from stopping
On the Iowa Gambling Task, cocaine and methamphetamine groups developed less advantageous choices than controls across successive blocks. Alcohol-group differences were less consistent across the task, appearing in later blocks. Comparisons between the substance-dependent groups did not establish significant differences in their learning rates.
By contrast, the study did not establish a group difference in stop-signal response inhibition. This null finding must accompany the decision-making findings: performance on a virtual card-choice task cannot be substituted for the ability to cancel an initiated response.
The stop-signal analysis also excluded 30 participants who failed to inhibit on more than 80% of stop trials. Results therefore apply to the analyzed subset, not automatically to all 134 recruits. Exclusion can change the composition of the sample whose stopping time can be estimated.
Working memory and switching were more nuanced
The methamphetamine and cocaine groups performed less accurately on a visuospatial working-memory task than controls. The group difference did not grow significantly with increased memory load. Methamphetamine participants also made more errors than the other substance-dependent groups on this measure.
On the switching task, methamphetamine and cocaine participants were slower than controls, but the additional cost of switching did not differ significantly by group. General slowing is therefore distinct from a selectively increased switching cost.
Wisconsin Card Sorting perseverative errors did not show significant group or sex effects after adjustment. A positive result on one flexibility measure does not authorize labeling every flexibility outcome abnormal.
How strong was the sex finding?
The paper discussed poorer gambling performance among women in the stimulant groups. However, the task-block-by-group-by-sex interaction was a trend, reported as p < 0.055. That qualification matters: it should not become a confirmed, universal claim that methamphetamine affects women more severely.
Small subgroups, varying task denominators, multiple comparisons and observational selection all constrain interpretation. Adjustment for age and education does not establish that substance exposure caused the differences or remove every premorbid influence.
The practical lesson is to name the exact domain and outcome. This historical study supports a differentiated profile, including genuine null comparisons, rather than a single impairment label applied to an individual.
Historical primary source
Van der Plas EAA, Crone EA, van den Wildenberg WPM, Tranel D, Bechara A. Executive control deficits in substance-dependent individuals: A comparison of alcohol, cocaine, and methamphetamine, and of men and women. Journal of Clinical and Experimental Neuropsychology. 2009;31(6):706–719. doi:10.1080/13803390802484797.
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