Given the extensive media attention granted to findings that suggest detrimental effects of cannabis on cognition (particularly your IQ), brain function, and mental health, you would be forgiven for thinking to smoke a spliff was akin to repeatedly bashing yourself over the head with a giant bong.
Whether or not using cannabis can lead to cognitive impairment is a hot topic of research and public interest.
However, since much of the work to date is cross-sectional (that is, measurements are taken only at one time in a person’s life), we cannot know whether cannabis users would have performed any differently before they started using cannabis. In short, we’re faced with a classic “chicken or egg” problem.
Another problem with current research is due to the simple fact that cannabis use does not occur in a vacuum.
The evidence suggests that those who start using cannabis from a young age often have less stable backgrounds and more behavioral problems than their non-using peers.
Teenage marijuana use also typically goes hand in hand with other drug use and risky lifestyle choices in general. It’s just difficult to control for all these other factors.
Claire Mokrysz, a Ph.D. student at University College London, is investigating whether teenagers is especially susceptible to harm from cannabis and alcohol use. She was able to conduct a study that could compare IQ over different ages in the same people.
At first look her results suggested that those teenagers who had used cannabis performed worse on their teenage IQ tests, after accounting for their ‘baseline’ IQ at eight years old.
Even those who had only used cannabis a handful of times scored roughly 2 IQ points lower than those who had never tried marijuana.
So at first glance, cannabis use was making teens less intelligent.
However, we also noted that the teenagers who had used marijuana were much more likely to have used cigarettes, alcohol, and other illicit drugs, and all these factors also predicted lower teenage IQ scores.
The more Mokrysz looked at the data, the clearer it was that cannabis was not such a clear-cut culprit when it came to lowering young people’s IQ scores.
But while her study is by no means definitive, it does highlight that we should all be more cautious when jumping to conclusions about the harms of a drug before we have substantial evidence either way.
Overly forceful conclusions about the potential adverse effects of cannabis are unscientific and based on an incomplete evidence base.
This can lead to the unfair marginalization of teenagers who use cannabis, which is the last thing we would want, given that this group is likely to include some of the most vulnerable in society.