Western University researchers found marijuana poses serious consequences for teens, but not adults

By Jonathan Sher,



Turns out getting stoned on marijuana carries much more dire consequences for teenagers than for adults -- at least if you're a rat and part of a new study released Monday by researchers in London.

Researchers at Western University’s Schulich School of Medicine & Dentistry have published a study that shows that the psychoactive component of marijuana caused long-term harm on the adolescent brains of rats, producing changes similar to what is found in schizophrenia.

“Adolescence is a critical period of brain development and the adolescent brain is particularly vulnerable,” said Steven Laviolette, a professor in the departments of anatomy and cell biology, and psychiatry. “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.”

After adolescent rodents were exposed to delta-9-tetrahydrocannabinol (THC) – the psychoactive component in marijuana – researchers found substantial and persistent behavioural, neuronal and molecular changes that are identical to neuropsychiatric conditions, such as schizophrenia.

Adolescent rodents with THC exposure were socially withdrawn, and had increased anxiety, cognitive disorganization and abnormal levels of dopamine – all factors present in clinical populations of schizophrenia.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, researchers say that pot should be kept out of the hands of teens.

“Our research improves our knowledge of how adolescent exposure to THC may lead to the onset of schizophrenia in adulthood,” lead author Justine Renard said. “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.”

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.