Can Reported Methamphetamine Use History Predict Who Has Cognitive Impairment?

In one abstinent cohort, commonly reported methamphetamine-use characteristics did not distinguish cognitively impaired from unimpaired participants. Use history supplied context, but it was not an adequate substitute for direct neuropsychological assessment.

The comparison reduced some major confounders

Cherner and colleagues evaluated 54 methamphetamine-dependent participants and 46 demographically comparable controls. Participants were free of HIV and hepatitis C infection, and groups had similar education and reading ability. The methamphetamine group had been abstinent for an average of 129 days. This was observational human research, not an administration experiment.

A group difference did not create a within-group predictor

The dependent group showed higher rates of neuropsychological impairment in most tested areas. Within that group, however, 22 impaired and 32 unimpaired participants did not differ in self-reported age at first use, years of use, administration route or abstinence duration. Demonstrating a group association and predicting which individual is impaired are distinct tasks.

The motor finding needs its statistical qualification

Greater past-year use was associated with motor impairment in an exploratory comparison, but the reported association did not remain significant after multiple-comparison adjustment. It should not be presented as a confirmed exception while omitting that correction.

What an evaluator should retain

Self-report can misestimate quantities and timing, and abstinence duration is not a quantitative measure of brain exposure. Background vulnerability and other factors may explain individual variation. Screening with urine and breath testing supported study procedures, but no specimen concentration threshold for cognitive impairment was established. The findings do not show that methamphetamine is harmless or that exposure can never relate to performance. They show why an individual’s functional ability requires assessment beyond a reported cumulative-use history.

Related evidence

For a different perspective on interpreting stimulant evidence, see our analysis of the Swedish amphetamine concentration study. Its study population and outcome should remain separate from the present findings.

Primary research

Methamphetamine Use Parameters Do Not Predict Neuropsychological Impairment in Currently Abstinent Dependent Adults. Original human research. doi:10.1016/j.drugalcdep.2009.08.010.