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Study Of Teen Twins Finds No Evidence Marijuana Lowers IQ

DENVER (CBS4) - A major concern of legal marijuana in Colorado and elsewhere is its accessibility to underage adolescents. Its effects on development are not fully understood, but a new study published in the Journal of Psychopharmacology may have at least one answer.

After studying twin siblings, scientists concluded that there is no evidence between cannabis use and a lowered IQ among teens, Sciencemag reports.

Similar previous studies were criticized for a short-term snapshot as opposed to a long-term study, or for not considering environmental factors. This study analyzed long-term marijuana use for 789 pairs of adolescent twins, one who used and one who did not, over 10 years. Participants took five intelligence tests and surveys about marijuana use over the 10 years of study. Twins share the same genes and have the same upbringing, creating an even baseline.

It was found that marijuana users lost roughly four IQ points over the course of the study, however, their twin sibling showed a similar pattern of decline. This suggests that factors other than marijuana use, such as school or home life, played a role in the lowering IQ.

Additionally, compared with teens who had used cannabis fewer than 30 times, those who used it for six months or longer did not show any difference in IQ change.

Critics say the study should have more specifically accounted for the frequency and quantity of marijuana use, and that although marijuana may not erode IQ, it does not mean that it is problem-free for adolescents.

RELATED STORIES: Marijuana Legalization Story Archive

In Colorado, there are concerns about teens having easy access to legal recreational marijuana, particularly edibles. The first annual report by the state on legal marijuana was released last February.

More recently, federal authorities released statistics showing negative results of legalization in Colorado.

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