Dianne McIntosh is continually alarmed by the teens who come into her Vancouver office telling the psychiatrist that they use cannabis to treat their mental-health issues because it's a natural – and harmless – substance.

"It's a natural product? So is tobacco, so is alcohol, these are all natural products," Dr. McIntosh said. With the federal Liberal government saying cutting down on teen cannabis use is a core reason it is pushing to legalize the drug next year, Dr. McIntosh and a panel of three other experts are gathering in Richmond, B.C., Sunday to clear the air about the dangers young people face when using the substance.

Chief among the messages that need to get out, she says, is the fact that even though a direct link has yet to be proven between using the drug and mental-health issues, evidence shows the substance can trigger psychotic episodes and negatively affect youth with a family history of mental illness, such as schizophrenia.

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Read more: With legalization coming, schools and health officials struggle with how to talk to teens

About 15 per cent of Canadians – including roughly 30 per cent of adolescents and young adults – report using cannabis in the past year, according to surveys.

Roughly 1 per cent of the overall population develop schizophrenia, which affects one's ability to discern reality from fantasy, with young men typically developing it in their late teens, while young women often become affected in their early-to-mid 20s, Dr. McIntosh said.

Research has shown heavy cannabis use plays a "clear role in the early onset of psychotic disorders," she said, noting schizophrenia can develop up to six years earlier in young people who consume the substance regularly.

"Those six years earlier? This is the difference between poverty; relationships; having children," she said of those teens genetically predisposed to schizophrenia who start consuming cannabis heavily.

Deborah Conner, executive director for the BC Schizophrenia Society, which is playing host to the panel at its annual general meeting, said the non-profit organization and its 3,000 members support restricting access to recreational marijuana to anyone under 25 years old, which echoes the position of the Canadian Psychiatric Association.

That is the age when a person's brain is considered to have finished developing. "If you're 35 [without any mental illness] and you want to smoke pot, I don't care," Dr. McIntosh said.

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Dan Werb, director of the Toronto-based International Centre for Science in Drug Policy, said young people will continue to use cannabis regardless of whether or not they are allowed to by law.

He said comparing alcohol and cannabis use among teens is like picking your poison as to which is worse.

"On the one hand, it's possible cannabis has more deleterious effects on the developing brain, but that alcohol has more deleterious effects at the societal level when used among young people," he said.

Cannabis was deemed less dangerous than tobacco in a 2010 study that ranked 20 legal and illegal drugs based on the dependence, social and physical harms they caused. The report, published in the British medical journal The Lancet, ranked tobacco as more harmful than cannabis, while both were considered far less dangerous to users and the general public than heroin, cocaine and alcohol.

Under prohibition, young Canadians often find it hard to find reliable information about cannabis. Psychiatrists and addiction experts expect legalizing and regulating cannabis to help – not hurt – young people who suffer from mental illness or use the drug to self-medicate by opening up an honest public dialogue about the harms of using the drug.

Young Canadians are going to consume drugs, Dr. Werb said, so the goal should be reducing the more problematic forms of drug use and incentivizing less harmful substances.

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Cannabis should play a role in that fight, he argued.

"Young people are obviously inquisitive and looking to experiment, but I think most would be most comfortable with less harmful forms of drug use and that's why cannabis is generally a more known quantity," he said.