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

Researchers at Western University’s Schulich School of Medicine & Dentistry have published a study that shows that a key psychoactive component of marijuana harms adolescent 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.

His research, published in the January issue of Cerebral Cortex, comes as a critical time. Justin Trudeau’s Liberal government has promised to legalize pot, regulate its sale and remove possession of small amounts as a crime — but has not unveiled details about how such changes would be implemented.

That left a researcher like Laviolette some room to affect the public debate, and though some longtime pot smokers were quick to criticize his work, the London scientist actually supports legalization.

If the goal is to keep pot out of the hands of teens, Canada has failed — teenage usage rates here are among the highest in the industrialized world, he said. Taking pot out of the hands of criminal dealers may help reduce access by teens, he said.

“Clearly, criminalization doesn’t work,” he said.

Researchers have long known the harm that can be caused by the psychoactive component that produces a “high” — delta-9-tetrahydrocannabinol or THC for short. But Laviolette pushed that knowledge further, showing how, at the molecular level, THC affects the developing brain of adolescent rats.

His research team found neuronal and molecular changes identical to neuropsychiatric conditions such as schizophrenia. Adolescent rodents given THC were socially withdrawn and had increased anxiety, elevated levels of dopamine and an inability to filter out unnecessary information, all factors in schizophrenia. Changes persisted into adulthood.

“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,” Laviolette said.

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

“With the (rise) in adolescent cannabis use and (increasing) THC content in newer cannabis strains, it is critically important to highlight (risk) factors (with) exposure to marijuana, particularly during adolescence,” lead author Justine Renard said.

Asked about the study, Federal Health Minister Jane Philpott agreed the current system doesn’t work with teen use here the highest in the developed world.

“Our government’s commitment to legalize, regulate, and restrict access to marijuana will not only keep profits out of the illicit drug trade, it will ensure marijuana stays out of the hands of children and teens,” she wrote in an email to The Free Press.

About half of the people who seek help at the First Episode Mood and Anxiety Program at London Health Sciences Centre used marijuana, said its medical director, Dr. Elizabeth Osuch.

“It’s brilliant research,” she said of the study. Earlier research showed that adolescents who used marijuana had significantly lower IQs compared to non-users of those who started using pot after age 18.

Laviolette says marijuana isn’t all bad and that a second ingredient may have a beneficial effect, actually protecting the brain from psychosis. His team is researching cannabidiol.

But THC drives sales because it’s addictive, so what people buy often has much more THC than cannabidiol.

“The level of THC has increased exponentially since the 1960s and ’70s,” Laviolette said.

Now that the Western team better understands how THC changes the brain, they hope to find genetic markers that might make some people more vulnerable to its effects.

jonathan.sher@sunmedia.ca

Twitter.com/JSHERatLFPress

ISSUE AT A GLANCE