• The long-term neuropsychological effects of persistent nonmedical drug use are still unknown. In this study, 22 young men, all extensive "polydrug" users, were examined while free from drugs for an average of 60 days by means of the Halstead-Reitan Neuropsychological Test Battery. Their performance was compared to that of age-education-sex-matched neurologically intact medical patients and a similarly matched group of neurologically impaired patients.
Blind independent ratings of test protocols by two experienced clinicians judged 41% to 64% of the drug users, 11% to 26% of the medical patients, and 84% to 89% of the neurologic patients to be impaired. Interpretation of these results suggests that in some individuals, heavy "polydrug" use may be associated with neuropsychological dysfunction, which persists at least an average of two months beyond cessation of drug use.
Grant I, Mohns L, Miller M, Reitan RM. A Neuropsychological Study of Polydrug Users. Arch Gen Psychiatry. 1976;33(8):973-978. doi:10.1001/archpsyc.1976.01770080091009