Study: Marijuana use not linked to reduced IQ in teens

New scientific research has failed to find a strong link between cannabis and lowered intelligence in teenagers.

In a study published January 6 in the Journal of Psychopharmacology, researchers initially found a statistical association between cannabis use and decrease intelligence, but later found out throughout several variables that marijuana use by itself is not to blame.

“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 researchers wrote.

Experts examined the IQ tests of 2,235 teenagers born in the Bristol, UK area in 1991 and 1992. Subjects were tested at age 8, and once again at age 15. While teenage cannabis users experienced lower IQ scores and educational performance, they were also more likely to experience problems with family and use other drugs such as alcohol and tobacco.

The researchers concluded:

After adjustment to account for these group differences, cannabis use by the age of 15 did not predict either lower teenage IQ scores or poorer educational performance,” the researchers explained. “These findings therefore suggest that cannabis use at the modest levels used by this sample of teenagers is not by itself causally related to cognitive impairment. Instead, our findings imply that previously reported associations between adolescent cannabis use and poorer intellectual and educational outcomes may be confounded to a significant degree by related factors.

Claire Mokrysz, lead author of the study, said researchers need to take many factors into account when examining the effects of cannabis.

“People often believe that using cannabis can be very damaging to intellectual ability in the long-term, but it is extremely difficult to separate the direct effects of cannabis from other potential explanations,” Mokrysz . “Adolescent cannabis use often goes hand in hand with other drug use, such as alcohol and cigarette smoking, as well as other risky lifestyle choices. It’s hard to know what causes what- do kids do badly at school because they are smoking weed, or do they smoke weed because they’re doing badly? This study suggests it is not as simple as saying cannabis is the problem.”

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