Dr James White from the Centre for the Development and Evaluation of Complex Interventions for Public Health Improvement (DECIPHer) examined data from just under 8000 people in the 1970 British Cohort Study, a large ongoing population based study, which looks at lifetime drug use, socioeconomic factors, and educational attainment.
The IQ scores of the participants were measured at the ages of 5 and 10 years, using validated scales, and information was gathered on self reported levels of psychological distress and drug use at the age of 16, and again at the age of 30.
Drugs assessed at 16 included cannabis and cocaine; and at 30 years of age included cannabis; cocaine; amphetamines; and ecstasy.
By the age of 30, around one in three men (35.4%) and one in six women (15.9%) had used cannabis, while 8.6% of men and 3.6% of women had used cocaine, in the previous 12 months. A similar pattern of use was found for the other drugs, with overall drug use twice as common among men as among women.
Men with high IQ scores at the age of 5 were around 50% more likely to have used amphetamines, ecstasy, and several illicit drugs than those with low scores, 25 years later.
The link was even stronger among women, who were more than twice as likely to have used cannabis and cocaine as those with low IQ scores. The same associations emerged between a high IQ score at the age of 10 and subsequent use of cannabis, ecstasy, amphetamines, and cocaine, although this last was only evident at the age of 30.
Dr White, School of Medicine, who led the research, published in the Journal of Epidemiology and Community Health, said: “Although most studies suggest that higher child or adolescent IQ prompts the adoption of a healthy lifestyle as an adult, other studies have linked higher childhood IQ scores to excess alcohol intake and alcohol dependency in adulthood.
“Although it is not yet clear exactly why there should be a link between high IQ and illicit drug use, previous research has shown that people with a high IQ are more open to new experiences and keen on novelty and stimulation.
“There is a clear need for future epidemiological and experimental studies to explore these and other pathways.”
Recognised risk factors for drug use, such as, levels of anxiety/depression during adolescence, parental social class, level of education, social class at 30 years and monthly income were all taken into account during analysis of the study’s findings.