Exposure to marijuana in adolescence causes schizophrenia-like changes in the brain

Researchers have published a study showing the significant, long-term impacts of delta-9-tetrahydrocannabinol (THC) – the psychoactive component in marijuana – on the adolescent brain.

After adolescent rodents were exposed to THC, researchers noted substantial and persistent behavioural, neuronal and molecular changes that are identical to neuropsychiatric conditions, such as schizophrenia. In contrast, adult rodents exposed to THC in the same study did not show the same changes.

The research was conducted by Steven Laviolette, PhD, professor in the departments of Anatomy and Cell Biology, and Psychiatry, lead author Justine Renard, PhD, and a team of researchers at Schulich School of Medicine & Dentistry and the School’s Addiction Research Group.

Researchers identified and performed tests in areas of behaviour that are commonly observed in schizophrenia and other neuropsychiatric disorders, such as social interaction, motivation and cognition, exploratory behaviours, levels of anxiety, cognitive disorganization (the inability to filter out unnecessary information), and various neuronal and molecular changes.

Adolescent rodents with THC exposure were socially withdrawn, and had increased anxiety, cognitive disorganization and abnormal levels of dopamine – all factors present in clinical populations of schizophrenia. These changes continued into early adulthood, well past the initial exposure.

Adult rodents showed no harmful long-term effects, though both adolescents and adults exposed to THC experienced deficits in social cognition and memory.

With the common use of marijuana by teenagers and the federal government’s move toward legalizing marijuana, Laviolette sees clear implications for his research. “Adolescence is a critical period of brain development and the adolescent brain is particularly vulnerable,” said Laviolette. “Health policy makers need to ensure that marijuana, especially marijuana strains with high THC levels, stays out of the hands of teenagers. In contrast, our findings suggest that adult use of marijuana does not pose substantial risk.”

“Our research improves our knowledge of how adolescent exposure to THC may lead to the onset of schizophrenia in adulthood,” said Renard. “With the current rise in adolescent cannabis use and the increasing THC content in newer cannabis strains, it is critically important to highlight the risk factors associated with exposure to marijuana, particularly during adolescence.”