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Higher IQ Linked to Illegal Drug Use in Adulthood, Study Finds

A high childhood IQ may be linked to illegal drug use in adolescence and adulthood, according to research published today in the Journal of Epidemiology and Community Health.

Researchers at Cardiff University and University College London based their findings on data from about 8,000 people included in the 1970 British Cohort Study, which has tracked 16,571 babies born in April 1970. Across most illegal drugs, men and women at age 16 and 30 who reported using drugs had a significantly higher IQ score at age 10 than those who reported no use, according to the researchers.

Participants were asked about use of substances including cannabis, cocaine, amphetamines, ecstasy, LSD, hallucinogenic mushrooms, crack and heroin. In a previous analysis of participants in the cohort, high IQ scores at 10 years were associated with an increased risk for excessive alcohol intake and frequent drinking episodes as an adult.

“A possible pathway that emerges from the literature on personality is that high IQ individuals have also been shown to score highly on tests of stimulation seeking and openness to experience,” the researchers said in the article.

At age 30, the 35.4 percent of men who said they’d used cannabis, the most favored drug, in the last 12 months, had a mean IQ of 104.65, compared with 99.04 among those who reported no use. Among women, the 15.9 percent who reported cannabis usage had a mean IQ of 105.73, compared with 98.10 among those who said they abstained.

Drug use was not tracked between ages 16 and 30, during which time participants could have started and stopped using, the researchers said.

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