Marijuana use among teenagers and young adults is rising, and those who use cannabis frequently could be harming their brains.
“It needs to be emphasized that regular cannabis use, which we consider once a week, is not safe and may result in addiction and neurocognitive damage, especially in youth,” Krista Lisdahl from University of Wisconsin-Milwaukee says in a press release. "The adolescent period is a sensitive period of neurodevelopment," she adds.
The negative effects of frequent use include cognitive decline, poor attention and memory, and decreased IQ, according to researchers presenting on the potential public health impacts of marijuana legalization at the annual American Psychological Association convention last week in Washington, D.C.
According to a 2012 study, 6.5 percent of high school seniors reported smoking marijuana daily -- that’s up from 2.4 percent two decades earlier -- and nearly a third of young adults ages 18 to 25 reported using marijuana at least once during a one-month period.
A recent study of 1,037 participants, who have been monitored since their birth until they were 38 years old, found that people addicted to marijuana can lose an average of six IQ points by adulthood. Brain imaging studies of regular users show significant changes in their brain structure, particularly among adolescents. Abnormalities in the brain’s gray matter (associated with intelligence) have been found in 16 to 19-year-olds who increased their marijuana use in the past year.
Researchers also recommend that legislators consider regulating levels of the major psychoactive chemical in marijuana, tetrahydrocannabinol (THC), to reduce the neurocognitive effects. “This relationship between marijuana and mental illness may be moderated by how often marijuana is used and potency of the substance,” says Alan Budney of Dartmouth. Some legalized forms of marijuana have higher levels of THC than other strains.
Furthermore, acceptance of legalized medical marijuana use appears to have an effect on adolescents’ perception of the risks, according to Bettina Friese of the Pacific Institute for Research and Evaluation. A 2013 study of 17,482 teenagers in Montana found that teenage marijuana use was higher in counties where more people voted for legalization in 2004. "People don't perceive it as a very harmful substance, and these community norms translate to teens," Friese says.