Marijuana Does Not Lower IQ in Teens

It’s common knowledge that about half of Americans use cannabis at least once in their lives and this takes place when they are teenagers. This has led to studies that have suggested that its use could harm the developing adolescent brain and affect IQ. However, ascertaining its true risk is something that these studies have not been able to prove until now.

In the study – the very first of its kind – the long-term use of marijuana in teens has been analyzed in detail, and for good reason too. In particular, the IQ of twin siblings who either used or stopped using marijuana were compared. As a result, no link between lower IQs and marijuana was found.

teenager_girl iq

Another study conducted by Valerie Curran at the University College in London among 2000 British teenagers that weren’t twins reached a similar conclusion. Published in the Journal of Psychopharmacology last month, the study also admitted to certain limitations as well.

Apart from this, George Patton, a psychiatric epidemiologist at the University of Melbourne, clearly stated that this barely proves that marijuana, when used heavily, is considered safe for teenagers.

Nicholas Jackson, lead researcher at the University of Southern California in Los Angeles, stated that previous studies that linked marijuana to lower IQ and memory loss only considered a “snapshot” in time. What this means is that it is difficult to prove whether these cognitive deficits are due to marijuana or just poor cognitive performance itself. This is why scientists has begun to follow large groups of marijuana users in order to ascertain whether it harms IQ or affects individuals in other ways.

The first of these studies was conducted in Dunedin, New Zealand, where significant declines in IQ was reported for those who used marijuana heavily between the ages of 13 and 38 years. Of course, the paper, while bringing to light the risks associated to using marijuana at an early age, failed to explain other reasons that could cause a decline in IQ such as dropping out of school or even their family environment.

teenager iq

One way by which one could deal with these limitations was to conduct studies on identical twins who share both upbringing as well as genes. So, for this new study, Jackson and his colleagues collected data from 789 pairs of twins from two separate studies conducted in Minnesota as well as Los Angeles, California.

Over a decade, the researchers conducted five intelligence tests as well as confidential surveys regarding the use of marijuana among these twin pairs between the age of 9 and 11. Questions about binge drinking, cocaine and opioid painkillers were also asked.

What was found was that while marijuana users lost 4 IQ points, their twins who abstained showed a similar pattern of decline too. Apart from this, those who used marijuana for six months or longer did not show decline in IQ, which was no different from those who used pot less than 30 times in all. This led to the conclusion that there is no link between marijuana increasing the risk of cognitive decline.

That said, there were certain flaws with this study – a lack of detail when it comes to how often and how much marijuana is used by the teens. Both the Minnesota and Los Angeles studies used different questionnaires too. Still, there’s no doubt that there is no connection between the two.

Of course, the best way to study marijuana’s effects on teens is to administer the drug to each individual and see how the dose, frequency and duration affects the brain.

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