Chronic drug use and cognitive impairments.

Reports regarding the effects of chronic drug use on human cognition and comparisons of different drug user groups have been inconsistent. Methodological flaws may account for some inconsistencies. To determine the effects of chronic drug use on cognition, drug users (n=192) were tested 17.1+/-0.3 days (mean+/-S.E.) and 99.4+/-1.7 days on average after their last use of drugs before beginning treatment. Drug users were categorized as stimulant, alcohol, or polydrug users. Their performance on tests of academic achievement, verbal memory, and abstraction was compared to performance of community-dwelling controls (n=137). The groups were matched on selected demographic and psychiatric characteristics. Historical records of achievement test scores were used to attempt to control for premorbid intellectual ability. Drug users showed impairments on each of the achievement tests (P<.001), as well as poorer total recall (P<.01) and abstraction ability (P<.05). Stimulant users performed worse on several tests relative to the other drug use groups. Only one of six tests demonstrated improvements following about 3 months of abstinence. Thus, chronic drug use is associated with cognitive impairments that do not improve substantially even after several months of abstinence.