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federal election 2015

Medical marijuana clone plants are shown at a medical marijuana dispensary in Oakland, Calif., Feb.1, 2013.Jeff Chiu/The Associated Press

Is cannabis, as Conservative Party Leader Stephen Harper claims, "infinitely worse" than tobacco, a substance that kills tens of thousands of Canadians each year?

Definitely not, say medical researchers and addiction experts, who are refuting Mr. Harper's provocative comparison between cigarettes and marijuana.

Mr. Harper has routinely brought up marijuana as a campaign issue, contrasting his government's tough stance against the drug with the Liberals' and Greens' plans to fully legalize it and the NDP's pledge to at least decriminalize it and study legalization.

When quizzed Saturday on his party's repeated opposition to making pot legal, Mr. Harper said that tobacco "does a lot of damage" but cannabis "is infinitely worse and it is something that we do not want to encourage."

The Canadian Cancer Society says smoking tobacco continues to be the leading preventable cause of premature deaths in the country, claiming about 37,000 lives each year. The non-profit organization says tobacco is the main risk factor for cancer, heart disease, stroke and lung disease in Canada.

In contrast, no deaths have been directly attributed to cannabis use or overdose, says Dr. Tim Stockwell, director of the University of Victoria's Centre for Addictions Research. But it is likely a factor in "a few" fatal crashes and "a few" lung-cancer deaths each year, he said.

"It's not a harmless herb, but the mortality rate is dwarfed by that of tobacco," Dr. Stockwell said.

He said cannabis was also 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 others than heroin, cocaine and alcohol.

Dan Werb, director of the Toronto-based International Centre for Science in Drug Policy, said research also shows there is a "massive disparity" between how easy it is to get addicted to each substance. Studies show 68 per cent of smokers become addicted over their lifetime, while about 10 per cent become dependent on cannabis, he said.

"If we are prohibiting drugs based on their addictive potential, then tobacco would be the first to be prohibited as it, by some estimates, has a greater addictive potential than heroin," he said.

Dr. Werb said evidence that showed marijuana damages lungs or the heart is "highly equivocal," whereas tobacco has been proven to be very damaging.

M.J. Milloy, an infectious-disease epidemiologist who is studying the therapeutic effects of marijuana at the B.C. Centre for Excellence in HIV/AIDS, also rebuked Mr. Harper for his claim that there are "overwhelming and growing scientific and medical evidence about the bad long-term effects of marijuana."

Dr. Milloy said there are obvious short-term risks, such as driving when using cannabis, but there is no evidence that moderate, long-term pot use incurs substantial health costs.

Some research has linked teens' long-term use of pot heavy with the psychoactive THC compound to mental-health issues such as psychosis and schizophrenia. But Dr. Milloy said no causal link has been proven and these young people might be genetically predisposed to such mental-health issues.

Still, there is growing evidence that adolescents and young adults "should be very careful if they choose to use marijuana" because their brains are still developing, he said.

A Conservative Party spokesman said Mr. Harper is against Liberal Leader Justin Trudeau's plan to legalize marijuana and introduce a regulatory system, as with alcohol and tobacco. The Conservatives state that such an approach only makes the drug more accessible to kids and cite figures showing their anti-drug strategy helped produce an overall decline in pot smoking among Canadian youth over the past decade.

A 2013 Unicef report showed just over a quarter of Canadian 15-year-olds had reported smoking cannabis in the past year, down from 37.5 per cent a decade earlier.

Dr. Werb said younger Canadians had been smoking less and less pot way before the Conservatives gained power in 2006 because of cultural, not political, forces.

Richard Johnston, a political science professor at the University of British Columbia, said Mr. Harper's approach is likely aimed at appealing to his party's morally-conservative base while trying to exploit the issue as a way of underscoring the narrative of his rival Mr. Trudeau being a novice and "not really a responsible player."

"Even though a majority of Canadians support [legal marijuana], the devil is always in the details," Prof. Johnston said. "[The Conservative approach to cannabis] is consistent with [their] broad moral posture that the country needs to have its backbone stiffened."