Marijuana use during adolescence may have detrimental effects on the brain and could even raise the risk for psychiatric disorders -- at least in mice, according to a new study.
Researchers from the University of Maryland School of Medicine found that marijuana use in adolescence seems to have an effect on the brain's cortical oscillations, which are patterns of neuronal activity in the brain. (In some psychiatric conditions like schizophrenia, for instance, these oscillations become abnormal.)
For the study, published in the journal Neuropsychopharmacology, researchers compared the cortical oscillations of two groups of adult mice. One group of mice was given no marijuana throughout its lifetime, while the other group of mice was regularly exposed to low doses of the active ingredient in marijuana for 20 days when they were young.
The mice exposed to marijuana when they were young had "grossly altered" cortical alterations, study researcher Sylvina Mullins Raver, who is a Ph.D. candidate in neuroscience at the university, said in a statement: "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."
However, when researchers tried the experiment again, this time instead administering marijuana to mice when they were already adults instead of when they were young, they didn't find any abnormalities in their ability to perform cognitive behavioral tasks, nor in their cortical oscillations.
"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," the senior author of the study, Asaf Keller, Ph.D., who is a professor of anatomy and neurobiology at the university, said in a 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."
Of course, the new study was conducted only in mice and further research is needed to see if the findings hold true in humans. But still, they could help to inform future research on psychiatric conditions and whether it's possible to reverse the effects of cortical oscillation changes, Keller noted.
However, yet another study from researchers at the University of California, San Diego, showed that teen marijuana use doesn't seem to have detrimental effects to the health of brain tissue, while regular alcohol use in teens does. However, that study did not test cognitive performance, and only involved looking at brain scans.