Marijuana legalization will harm the health of youth unless major changes to the proposed law are made to protect their developing brains, a medical journal editorial says.

Dr. Diane Kelsall, interim editor in chief of the Canadian Medical Association Journal, says Bill C-45 fails to safeguard vulnerable youth.

"There are a number of things in the legislation that are truly worrisome," Kelsall said in an interview. "If the intent is truly a public health approach and to protect our youth this legislation is not doing it."

Canadian young people ranked first for cannabis use in North America and Europe, with one-third saying they tried it at least once by age 15, the Canadian Pediatric Society says.

Before the federal election, physicians said the right legislation to legalize pot might curb teen toking by restricting access.

The editorial takes issue with several aspects of the bill, which:

Sets the minimum age to buy recreational marijuana at 18. Kelsall calls that too young given evidence suggesting that the human brain doesn't mature until about age 25.

Allows people to grow pot at home, which Kelsall said increases the likelihood of diversion to young people.

Lacks national standards for retail distribution.

Lacks limits on potency of strains despite increased risk of harmful effects with higher-strength cannabis.

"From my perspective, from my colleagues' perspective, this legislation is being pushed through," Kelsall said. "We're just very worried that we're conducting a national experiment and unfortunately the guinea pigs are kids."

On Monday, Health Minister Jane Philpott was asked by reporters if she was prepared to change the age.

"Provinces and territories will have the opportunity to address the age," Philpott said. "Our bill is not entirely through the legislative process. It is possible that it could change along the way."

Making a product legal does not mean it is advisable or recommended, Philpott said.

Marijuana as a psychosis trigger

At the Centre for Addiction and Mental Health in Toronto, psychiatrist Romina Mizrah uses PET scanners to study how cannabis use changes brain function in young people with an average age of 20.

In young people who regularly use cannabis, preliminary evidence points to a reduction in an enzyme that regulates the endocannabinoid system that buffers key chemistry within the brain, said Mizrahi.

"There is some understanding at this point from epidemiological studies that certainly marijuana is a trigger," said Mizrahi, director of the Focus on Youth Psychosis Prevention program. "Marijuana use predates the psychosis. Whether it causes the psychosis, that's a different question and that we don't know."

Studies using MRI scanners also show physical and functional changes in the developing brains of regular users that are associated with damage, Kelsall said.

More potent pot

Mike Stroh, 35, of Toronto says he's part of a generation who grew up smoking current strains of marijuana, which have been genetically selected to produce a powerful high, with THC levels of about 20 per cent. That's up from around seven per cent in the 1960s and '70s.

From age 13, Stroh got high almost daily until age 30.

"I was into sports," Stroh recalled. "I wanted to do stuff at school, but I wouldn't make it to the practice, I wouldn't make it to the tryouts, because I was either up all night selling drugs, trying to get them, fall asleep in a drug-induced coma, and then wake up in a mess."

Mike Stroh with his kids. Stroh is now a mental-health advocate who wants to show recovery is possible. (Mike Stroh)

Stroh also lived with depression and anxiety and said he was never able to like himself. "That's the torment that brought me to my knees."

He felt robbed of being himself and the opportunity for emotional maturity, cognitive development and professional opportunities.

"Because marijuana doesn't bring you to your knees as quickly as other drugs may … there's this illusion that because you can be high and do things, it's not bad, so to speak."

Stroh is now a mental health advocate who draws on his personal and family experiences to educate.

"We need to teach kids how to take care of themselves so when they do feel anxious and do feel depressed, scared or … frustrated with life, because yes, that's a part of being a teenager, then they learn that there's so many things they can do to help themselves as opposed to use drugs."