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Study: Marijuana Use Doesn't Cause Lower IQ, Test Scores Among Teens

A new study in the UK has found that there is no strong causal link between teens using cannabis and a decrease in their intelligence and school performance.

The study by researchers at the University College London was based on 2,235 teens who were part of another project, the Avon Longitudinal Study of Parents and Children, reports PsyPost.

The study, which was published in the Journal of Psychopharmacology in January, said that the children had their IQs tested at ages 8 and 15. Nearly 25 percent of them said they had smoked cannabis at least one time, while 3.3 percent had used it at least 50 times.

While the cannabis users did score lower in IQ and educational test scores, there was no proof that cannabis directly caused either.

The IQ scores of teens who used cannabis more than 50 times were only 0.1 point lower than those who had never tried it. These heavy users also had slightly lower test scores.

Claire Mokrysz, the study's lead author, noted: “The notion that cannabis use itself is causally related to lower IQ and poorer educational performance was not supported in this large teenage sample.”

The study also found that cannabis users had a higher chance of experiencing childhood problems and using other drugs, such as alcohol and cigarettes.

The study concluded:

"There is much debate about the impact of adolescent cannabis use on intellectual and educational outcomes ... These findings suggest that adolescent cannabis use is not associated with IQ or educational performance once adjustment is made for potential confounds, in particular adolescent cigarette use. Modest cannabis use in teenagers may have less cognitive impact than epidemiological surveys of older cohorts have previously suggested."

Sources: PsyPost, Journal Of Psychopharmacology / Photo credit:

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