Intelligent children are more likely than their less intelligent peers to use illegal drugs in later life, according to a study which has found a link between high IQ scores and drug use.
Children who were in the top third in terms of IQ when aged 5 and 10 were found to be at significantly increased risk of taking illegal drugs such as cannabis and cocaine when they became older.
The study was based on interviews with nearly 8000 people who were part of the 1970 British Cohort Study, which involved measuring IQ scores when each child was 5 and 10, and asking them about their drug habits when they were 16 and 30.
By the age of 30, around one in three men (35.4 per cent) and one in six women (15.9 per cent) had used cannabis while 8.6 per cent of men and 3.6 per cent of women had used cocaine in the previous 12 months, the study found.
A similar pattern was found for other drugs, such as barbiturates, LSD and heroin. Boys in the top third in terms of IQ when aged 5 were about 50 per cent more likely than the bottom third to have used drugs such as amphetamines and Ecstasy when aged 30.
The effect was even stronger among women. High-IQ women were more than twice as likely as low-IQ women to have used cannabis and cocaine in the past year, for instance.
Dr James White of Cardiff University, who led the study published in the Journal of Epidemiology and Community Health, said that because the effect could be picked up at the age of 5, before schooling, it might be independent of education.
"The study just looked at whether you had or had not used drugs in the last year. We don't know the level of usage and we don't know the harm of low-level drug use.
White suggested that one possible explanation was that more intelligent people were more likely to get bored or to suffer at the hands of their peers, either of which could lead to experimenting with drugs.
Overall, he added, high-IQ people were more likely to have healthier lifestyles because they were better informed about diet and exercise.