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Various medical marijuana products are distributed as an alternative to intravenous drugs at an overdose prevention site in Vancouver, B.C., on Aug. 28, 2017.Rafal Gerszak

Consuming cannabis every day could delay at-risk youth from moving on to injecting more dangerous drugs, according to a new study that casts doubt upon the age-old assumption that marijuana acts as a gateway for teens to try other more harmful substances.

The research, from scientists at the BC Centre on Substance Use, also adds to other work that has suggested marijuana could be used as a substitute for people addicted to opioids

Researchers repeatedly interviewed 481 homeless young people in Vancouver’s downtown core who had never injected any drugs and found - over a decade of tracking this at-risk cohort - that daily cannabis use was associated with a 34 per cent decrease in the rate people started injecting drugs.

“One common perception about cannabis is that it’s a so-called gateway drug to other, higher risk drug use. However, our study found the opposite,” said M. J. Milloy, an infectious-disease epidemiologist at the centre and co-author of the study led by Hudson Reddon.

“For them, cannabis was a strategy that they used to try and manage their drug use – to try and ‘detox’ from harder opioids or stimulants.”

The research, drawn from the centre’s ongoing “At-Risk Youth Study” and published in the March issue of the Drug and Alcohol Review, involved people aged 14 to 26 who couch surfed or slept on the streets in and around Vancouver’s Granville Street and were interviewed over a median period of two years.

The average age of people who begin injecting these illegal drugs is between 19 and 23, with homeless young people more likely to start using these illicit substances, which makes them more likely to get infected with HIV or hepatitis C, overdose or engage in criminal activity, the study said. These youths are also more likely to engage in high-risk practices such as sharing needles, Dr. Milloy said.

The study follows other recent research that suggests cannabis may be a potential substitute for users of legal or illicit opioids, as well as crack cocaine.

Another study by the BC Centre on Substance Use tracked 122 people who consumed crack in and around Vancouver’s Downtown Eastside over a three-year period and found they reported using that drug less frequently when they opted to also consume cannabis.

Another recent study from the University of British Columbia and funded by licensed cannabis grower Tilray found more than half of the 271 medical-marijuana patients interviewed said they use cannabis to help them get off heavier prescription drugs, with the largest percentage saying pot acts as a substitute painkiller for opioids.

That research added to a small body of science that suggests patients are effectively using marijuana to replace opioids, a class of legal and illicit painkillers that has led to a crisis that killed more than four thousand Canadians last year.

As Ottawa gets set to legalize cannabis as early as this summer, addictions and public health experts such as Dr. Milloy have urged the federal government to consider the dangers – and potential benefits – that Canada’s example of ending prohibition can offer the world.

“Many scientists have long said that if we’re really looking at the trajectory of substance use, we must recognize that tobacco and alcohol are much more precursors of other substances than cannabis is,” Dr. Milloy said.

He said he is part of a team that is now hoping to apply for funding this summer to start a small controlled trial to see if cannabis’ substitutive effects can be proven.

The study released Thursday was funded by the American National Institutes of Health and the Canadian Institutes for Health Research.

Recreational cannabis is now legal in Canada. The federal and provincial governments have been working to develop rules on the use and sale of cannabis. Here are some things you should know about the use and sale in your province.

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