Purpose in life and coping skills are hypothesized to mediate association between cognitive abilities (e.g., fluid and crystallized intelligence) and polydrug use. Results indicated relationship between crystallized intelligence and alcohol use was mediated by purpose in life. Older age predicted higher cognitive abilities, stronger coping strategies, more polydrug use, less purpose in life. Cognitive abilities predicted less cigarette/illicit drug use. (Contains 38 references, 4 tables, and 4 figures.) (Author)