Regular marijuana use during adolescence, but not adulthood, may permanently impair
the brain and increase the risk for certain psychiatric diseases such as schizophrenia, according to an article published in the journal Neuropsychopharmacology.
“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,” senior author Asaf Keller said in a press statement. “Previous research has shown that children who started using marijuana before the age of 16 are at greater risk of permanent cognitive deficits, and have a significantly higher incidence of psychiatric disorders such as schizophrenia.
“There likely is a genetic susceptibility, and then you add marijuana during adolescence and it becomes the trigger,” he said.
Sylvina Mullins Raver, a Ph.D. candidate at the University of Maryland School of Medicine, said their study tried to determine whether there is a real, permanent health risk to marijuana use.
They began by examining cortical oscillations in mice. That means they examined the neuro activity that is believed to underlie the brain’s functions. These oscillations are abnormal in schizophrenia and in other psychiatric disorders. The scientists exposed young mice to very low doses of the active ingredient in marijuana for 20 days, and then allowed them to return to their siblings and develop normally.
“In the adult mice exposed to marijuana ingredients in adolescence, we found that cortical oscillations were grossly altered, and they exhibited impaired cognitive abilities,” Raver said in a press release. “We also found impaired cognitive behavioral performance in those mice. The striking finding is that, even though the mice were exposed to very low drug doses, and only for a brief period during adolescence, their brain abnormalities persisted into adulthood.”
The experiment was repeated on adult mice whose cortical oscillations remained normal.
“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 that 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.”
Keller’s team believes the results are applicable to humans.