After developing post-traumatic stress disorder during his second deployment in Afghanistan in 2007, Canadian army veteran Fabian Henry tried numerous anti-depressants to quell his suicidal thoughts and violent rages. For three years, he was on as many as nine pills a day. But only one drug worked for him: marijuana.

"It literally gave me relief and changed my life," says Henry, who now vaporizes 10 grams of medical marijuana a day. "I went from suicidal and homicidal ideation, to DUIs, to threatening to kill people, to beating people up, to doing yoga seven days a week, using cannabis and spending more time in nature with my kids."

Henry, who served 13 years in the army and carried out six deployments as a combat engineer, is now aiming to help other veterans and first responders with PTSD gain access to medical marijuana.

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Getting the health community to embrace marijuana as a treatment for PTSD, however, isn't easy. Thirteen years since Health Canada granted Canadians access to marijuana for medical purposes, doctors remain hazy about when, how and if they should prescribe it. Although a court ruling requires Health Canada to provide access to a legal source of marijuana when authorized by a physician, the government does not endorse its use. And groups such as the Canadian Medical Association and the College of Family Physicians of Canada note there is a lack of scientific evidence to show its therapeutic benefits.

To help narrow the evidence gap, Nanaimo, B.C.-based medical marijuana producer Tilray announced Thursday it has teamed up with researchers at the University of British Columbia's Okanagan campus to conduct the first clinical trial in Canada to test the impact of medicinal marijuana on PTSD sufferers. The study, which requires the approval of the university's ethics committee and Health Canada to proceed, would provide a rare controlled examination of the drug's efficacy in treating the disorder. And while some applaud the effort, not everyone believes such work is in the best interest of PTSD sufferers.

The Tilray-UBC study intends to recruit 40 veterans, first responders and victims of sexual assault with PTSD, and to administer various strains of marijuana or a placebo using vaporizers. If approved, researchers anticipate they can begin enrolling their first participants by spring and conclude their research by late 2016. Tilray is currently the sole funder of the study, which is estimated to cost $350,000, and will also supply the marijuana.

"We need more treatments for PTSD. There's too many veterans and victims of crime and first responders that are suffering, and the existing treatments don't work for a number of them," says Dr. Zach Walsh, one of the principal investigators of the proposed study and a psychology professor at UBC.

Brain-imaging studies indicate people with PTSD lack certain neurotransmitters in the brain's endocannabinoid system, a network that, in animal studies, has been shown to be involved in fear responses. The brains of PTSD sufferers, Walsh explains, "are hungry for cannabinoids," which cannabis may help satisfy.

According to Health Canada, statistics for patients who use medical marijuana to treat PTSD are not available – nor is the number of sufferers who self-medicate. But there's a huge demand among afflicted veterans and first responders, says Henry, who has helped more than 300 individuals access the drug since he opened his Oromocto, N.B.-based Marijuana for Trauma Inc. eight months ago. They come to him with a doctor's referral, and he helps them with the necessary paperwork to obtain the drug from a licensed producer and receive coverage from Veterans Affairs Canada.

Henry says his not-for-profit company was trying to help RCMP Cpl. Ron Francis obtain marijuana when he died by suicide in October. Francis, who suffered from PTSD, had criticized the force for not providing services for the disorder, and became known for using medical marijuana while in uniform.

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"This is what happens when you don't get this medicine," Henry says.

Psychiatrist Dr. Paul Sedge says while the proposed Tilray-UBC study would contribute to much-needed scientific research, he has serious concerns about the risks involved with using marijuana. While he acknowledges that his patients claim it reduces PTSD symptoms, Sedge does not believe it should be used to treat the disorder.

"There are many existing medications that have more science behind them … where research dollars may be better spent," says Sedge, a retired member of the Canadian Forces, who now works with veterans at at The Royal, a mental-health centre in Ottawa.

"The concerns are we know that marijuana is a substance of abuse and dependence," he says, adding that it's also associated with the onset of psychotic illness and mood and anxiety disorders, and can worsen the conditions of those who already have such illnesses.

"The comparison I would make is someone who has panic disorder or severe anxiety may find that when they have a drink of alcohol, it calms their nerves. But we would never prescribe alcohol to treat anxiety," he says. He suggests a safer solution may be found in synthetic endocannabinoids, such as Nabilone.

Research on marijuana's efficacy is scarce because of the administrative hurdles involved when testing a regulated substance, and finding a suitable placebo can be challenging, says Dr. Bernard Le Foll, a clinician-scientist at the Centre for Addiction and Mental Health in Toronto. "Very few investigators are willing to put the effort to go into those directions," he says.

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"The reality is that it is [in the] interests of the medical-marijuana grower to develop the evidence about the product they are selling," Le Foll says, adding that as long as the researchers of the proposed UBC-Tilray study have some independence from the company to develop their design, "it should not be problematic."

Philippe Lucas, Tilray's vice-president for patient and research services, says Health Canada's move this year to hand over the production and distribution of medical marijuana to multiple authorized producers opens the door to having companies like his support clinical trials.

"There's very few jurisdictions where this kind of work can take place without jumping through nearly insurmountable hurdles," Lucas says. "Research into the whole-plant medicine, like what we're authorized to produce and distribute to critically and chronically ill Canadians, is going to be, I think, a nearly uniquely Canadian phenomenon."