Study: previous research on cannabis use among teenagers «exaggerates» the risks

Fears that cannabis is causing irreparable damage to teenage brains have been fuelled by studies that have «overestimated» the effects on intelligence and other cognitive functions, according to a scientific study which found few side effects after 3 days of abstinence.

Numerous studies have shown that teenagers who used cannabis performed less well on tests of attention, memory, learning and organization than young people who used cannabis irregularly or abstained.

Researchers at the University of Pennsylvania conducted «the first quantitative synthesis of the literature focusing on cannabis and cognitive functioning in adolescents and young adults.»

The research team reviewed 69 previous studies, which compared 2152 frequent cannabis users with 6575 participants who reported minimal or no cannabis use.

Looking at all these studies, the researchers found «a small but significant effect of decreased cognitive functioning in adolescents and young adults who reported frequent cannabis use.»

The researchers then noted that some of these studies required all participants to abstain from cannabis use for at least 72 hours before taking the cognitive tests, while others allowed participants to continue smoking until the day before the tests. Studying these groups separately, the researchers found that adolescent users who had abstained for 3 days or more had the same results as non-users.

«Associations between cannabis use and cognitive functioning in cross-sectional studies of adolescents and young adults are weak and may be of questionable clinical significance for most individuals,» the researchers conclude. «Furthermore, abstinence for more than 72 hours decreases cognitive deficits associated with cannabis use. Although other findings (e.g. on psychosis) were not examined in the reviewed studies, the results indicate that previous studies of cannabis in youth may have overestimated the magnitude and persistence of cognitive deficits associated with [cannabis] use.»

«The deficits reported could reflect some residual effects of heavy consumption or cessation of consumption.»

The study concludes that «future studies should examine individual differences in susceptibility to cannabis-associated cognitive dysfunction».