Marijuana use in adolescence may cause permanent brain harm

BALTIMORE, July 25 (UPI) -- Regular marijuana use in adolescence, but not adulthood, may permanently impair brain function and cognition, U.S. researchers say.

Senior author Asaf Keller, a professor at the University of Maryland School of Medicine, said regular marijuana use in adolescence might also increase the risk of developing serious psychiatric disorders such as schizophrenia.

"Over the past 20 years, there has been a major controversy about the long-term effects of marijuana, with some evidence that use in adolescence could be damaging," Keller said in a statement.

"Previous research has shown that children who started using marijuana before the age of 16 were at greater risk of permanent cognitive deficits, and had a significantly higher incidence of psychiatric disorders such as schizophrenia."

Study co-author Sarah Paige Haughwout, a research technician in Keller's laboratory examined cortical oscillations -- patterns of the activity of neurons in the brain -- in mice.

Young mice were exposed to very low doses of the active ingredient in marijuana for 20 days, and then allowed to return to their siblings and develop normally. The experiment was repeated in adult mice never before exposed to the drug.

The study, published in the journal Neuropsychopharmacology, found cortical oscillations and ability to perform cognitive behavioral tasks remained normal in the adult mice, indicating it was only marijuana exposure during the critical period of adolescence that impaired cognition through this mechanism.

"We looked at the different regions of the brain," Keller said. "The back of the brain develops first, and the frontal parts of the brain develop during adolescence. We found the frontal cortex is much more affected by the drugs during adolescence. This is the area of the brain controls executive functions such as planning and impulse control. It is also the area most affected in schizophrenia."