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Claim of link between intelligence and cannabis use in adolescence provides fresh headache for researchers

Children with high and medium academic ability at age 11 are more likely to use cannabis in late adolescence compared to children with low academic ability, according to a new study published in BMJ Open.

The researchers, from University College London, examined the school records of more than 6,000 children. Their analysis showed that children of medium academic ability at age 11 were more likely to go on to be either occasional or persistent users of cannabis than children of low academic ability. This was the case for both early adolescence (13 to 17 years of age) and in late adolescence (18 to 20 years of age).

For children with high academic ability at age 11, the results were less certain. Although they were more likely than the low ability children to use cannabis in early adolescence, the difference between the two groups was not statistically significant. In other words the association could have been down to chance. However, for the period between 18 and 20 years, the high ability group was significantly more likely to be either occasional or persistent users of cannabis than the low ability group.

Previous research has found a clear link between academic ability and intelligence, so the evidence suggests that smarter kids are more likely to smoke cannabis than their less gifted peers. The big question is: why?

The authors of the BMJ report agree that their findings do not clearly identify the reasons why there is a link between academic ability and cannabis use in adolescence. However, the results of this latest study indicate that we might learn more if we turn this question on its head. Why are children with a lower academic achievement at age 11 less likely to smoke cannabis in late adolescence?

This opens up a new range of possible explanations for this link. For example, is low academic ability related to a low awareness of the possibilities to explore new experiences and a lesser willingness to challenge the orthodox beliefs of society compared to children of medium and high ability? This is still speculation – but it does identify a new set of questions for further research.

Cannabis - not as harmless as we once believed. OpenRangeStock/

Why do these findings matter?

Cannabis is the most popular prohibited drug in the UK. A 2016 Home Office survey reported that more than 1.8m people in England and Wales, aged between 16 to 24 years, had used cannabis at least once in their lives, although the figures for use in the past year (975,000) and the past month (476,000) were much smaller. Therefore, a significant minority of young people in the UK have used a drug which we now know to be associated with changes in the structure of the brain, with changes in the ways in which brain cells communicate with each other, and with poorer performance on some tests of mental abilities such as memory, among other problems.

If these new findings in the BMJ prompt us to think in a new way about the relationship between academic ability and cannabis use in adolescence, then they will have served a very important purpose. In science, as in life generally, identifying the most appropriate question is an important first step to finding the most useful answer.

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