Intelligence quotient in childhood and the risk of illegal drug use in middle-age: the 1958 National Child Development Survey.

Purpose: High childhood IQ test scores have been associated with increased alcohol dependency and use in adult life, but the relationship between childhood IQ and illegal drug use in later life is unclear. Methods: Participants were 6713 members of the 1958 National Child Development Survey whose IQ was assessed at 11 years and had their lifetime illegal drug use measured at 42 years of age. Results: In analyses adjusted for a range of covariates, a 1 SD (15-point) increase in IQ scores was associated with an increased risk of illegal drug use in women: ever using cannabis (odds ratio [OR], 1.30; 95% confidence interval [95% CI], 1.16–1.45), cocaine (OR, 1.66; 95% CI, 1.21–2.27), amphetamines (OR, 1.50; 95% CI, 1.22–1.83), amyl nitrate (OR, 1.79; 95% CI, 1.30–2.46) and “magic mushrooms” (OR, 1.52; 95% CI, 1.18–1.98). Associations were of lower magnitude in men. Conclusions: In this cohort, high childhood IQ was related to illegal drug use in adulthood