It's not official yet, but all signs point to Quebec letting people use cannabis at the same age as they are allowed to use alcohol: 18.

Leaked reports indicate the Liberal government will ban private sales of marijuana. As in Ontario, marijuana sales will be handled by a Crown corporation, likely the SAQ.

The age decision was apparently made in order to discourage the sale of marijuana on the black market to young adults, however that goes against the advice of health professionals, who say marijuana use is hazardous for developing brains.

"The adolescent brain is developing right up until the age of 25," said Dr. Patricia Conrod.

The psychiatry professor at the University of Montreal has examined 4,000 students at 31 high schools in the past four years.

Her research shows that marijuana use can lead to psychosis-related events in some youths.

"Our studies are also showing that early onset cannabis use is indeed a risk factor for psychosis-like experiences or symptoms particularly among people who have a psychological vulnerability towards those types of symptoms," said Dr. Conrod.

Another researcher, Dr. Dave Ellemberg, said there is evidence marijuana has a permanent effect on brain function.

"There's research backing this up, that after a while the brain is less efficient. Your memory is less efficient, you don't focus and pay attention as well," said Dr. Ellemberg.

There is disagreement about what is a safe age to use marijuana.

The federal government and the Canadian Pediatric Association recommended age 18, with the CPA saying most brain development has happened by that age.

The Canadian Psychiatric Association argues cannabis should be banned until age 21, and that until age 25 people should be limited in how much they can use, and the potency of its active ingredient, THC.

Quebec's opposition party the Coalition Avenir Quebec also prefers marijuana be banned for those under 21.

Dr. Conrod admits it's a tough job for governments if they set an age limit that is too high.

"What was shown in Colorado is that rates of youth incarceration, school expulsions, did go up after they legalized cannabis," she said.

Public Health Minister Lucie Charlebois is expected to table legislation concerning marijuana in the coming weeks.