A study published in the Journal of Psychopharmacology and conducted by the Avon Longitudinal Study of Parents and Children Cohort (ALSPAC). The study found that cannabis use in teens had no effect on IQ when compared to a group that reported never having used the sunstance. The study looked at 2,200 people, tested at ages 8 and 15, making it one of the largest studies to date. 

Tobacco use causes lower IQ’s

When controlling for cigarette and acohol use, mental health and beahviour problems, the ALSPAC study reveals that teenagers who has used cannabis over 50 times during the period, did not differ in IQ test performance versus their peers.

When the same controls were made for tobacco and alcohol use, it was found that those teenagers that used tobacco and alcohol showed a strong diminishing effect on their performance versus their peers.

Because of the overlap of cannabis users and tobacco users, it is very hard to reach findings in studies that look at both. This is why this study is so useful, because it used such a large pool of participants that it is still possible to draw conclusions from overlapping data sets.

These results could challenge the assumption that cannabis and not tobacco is the most harmful substance used by teenagers today.