Smoking cigarettes, drinking too much alcohol and smoking cannabis can be detrimental to your health. Misuse of these substances (with varying levels of usage) is responsible for negative health outcomes such as lung cancer, cirrhosis of the liver and psychiatric illnesses, respectively, as well as substance dependencies – all of which act as a massive burden on the NHS and a huge challenge for public health. Furthermore, usage of these three substances can lead to negative non-health outcomes such as poor educational attainment and unemployment.

Despite a downward trend in usage over the last decade, smoking cigarettes, drinking alcohol and smoking cannabis is still relatively common amongst UK adolescents. Some negative outcomes of usage can be exacerbated by early onset and targeting this demographic with health interventions may prevent them from developing diseases and dependencies and draining valuable public resources. This, however, requires an understanding of why teenagers engage in these behaviours.

Familial factors such as socioeconomic status; social factors such as peer pressure and bullying; individual factors such as depression and sexual orientation; all on top of the fact that teenagers’ brains are hardwired to engage in thrill-seeking behaviours – there is no clear cut answer as to why teenagers use substances.

One risk factor that is not well understood within the scientific community is the role of intelligence on adolescent substance use. This is why a colleague and I set out to research this link and whether KS2 scores at age 11 could be used to identify patterns of adolescent substance use. Our research concluded that brainier children were less likely to smoke cigarettes but more likely to drink alcohol regularly and smoke cannabis in their teenage years and into early adulthood.

What’s more, our research showed that these patterns persisted into later adolescence, providing evidence against a recent theory that suggests that smarter teenagers are more likely to experiment with substances early on in adolescence before giving up later.

Our study, published in the BMJ Open, analysed the data from a representative sample of over 6000 English school pupils followed from the age of 14-20 as part of the Longitudinal Study of Young People in England. Our findings that adolescents with high academic ability are less likely to smoke but more likely to drink alcohol regularly and use cannabis are broadly consistent with the evidence base on adults, but the reasons behind these associations are not fully understood.

Cognitive ability is largely associated with better life chances and healthier life choices, so one might expect smarter teens to stay away from substances. However, cognitive ability is also associated with openness to new experiences and higher levels of boredom due to a lack of mental stimulation in school and this combination may lead to experimentation with substances.

(Flickr - Leni Lunatic)
(Flickr – Leni Lunatic)

Another potential explanation is that more able children are known to be accepted by older peers, who may facilitate access to alcohol and cannabis. Furthermore, the persistent association with alcohol use may be related to parental influence, since parents with high cognitive ability and socioeconomic status are known to drink alcohol more regularly.

An unusual finding of the research was that the association between childhood academic ability and early adolescent cannabis use was non-linear, before developing into a linear association in later adolescence i.e. the medium ability group was more likely to smoke cannabis than the high ability group. A potential explanation for this phenomenon is that higher ability adolescents are more open to try cannabis but are initially cautious of illegal substances in early adolescence, as they are more aware of the immediate and long-term repercussions that breaking the law might incur than lower ability adolescents.

There are limitations to observational epidemiology. In our study we observed an association between childhood academic ability and adolescent substance use, and controlled for a range of factors such as age, sex, ethnicity, socioeconomic status and long-term illness. But this is merely correlation, not causation; we can’t be sure that the smartest kids will go on to use certain substances purely because they’re smarter. There are likely to be other factors involved that we just couldn’t account for in our study.

Moreover, we did not have access to contextual data on alcohol consumption (what type of alcohol was being drunk, what volume, and why?) or quantity of cannabis use – only if the young person had tried it in the last 12 months. Future observational studies should definitely aim to cover some of these areas to help get a better picture of what adolescent substance use looks like, not just why it happens.

Our finding that alcohol consumption and cannabis use amongst the highest ability participants persisted into early adulthood is interesting as it goes against previous research but the data available stopped at the age of 20. This limits the conclusions we can draw about how these patterns develop over time. The good news is that a follow up study using the same cohort of participants has been conducted, with the results at age 25 being released later this year, allowing for further analysis of this relationship.

We still have a lot to learn about why teenagers use certain substances and just how big of a player childhood intelligence is in this complicated, multifactorial issue. As ever, future research will help to elucidate this relationship and, in doing so, give health providers and public policy-makers a far better chance at tackling substance misuse in younger people and the negative outcomes they have on the individuals and on society.

James Williams is a fifth year medical student at University College London with an interest in Paediatrics and Adolescent Medicine.

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