Fewer Canadian veterans have sought prescription opioids and tranquillizers in recent years, while at the same time prescriptions for medical marijuana have skyrocketed.

It is not clear whether the two are related, but the trend echoes what researchers have found in U.S. states with medical-cannabis laws.

New data provided to The Globe and Mail by Veterans Affairs Canada show that over the past four years, the number of veterans prescribed benzodiazepines – with brands such as Xanax, Ativan and Valium – had decreased nearly 30 per cent. Opioid prescriptions also shrank almost 17 per cent during that same period.

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In a report last month, the Auditor-General warned Veterans Affairs to rein in spending on its coverage of medical marijuana. Government reimbursements for veterans' pot prescriptions had ballooned from fewer than a hundred patients costing $284,000 four years ago to more than 1,700 former soldiers charging the department $20-million last fiscal year.

This set of statistics is too small and unrefined to prove any concrete links between the use of the three drugs. But American research showing significant declines in opioid overdoses where medical marijuana has been legalized suggests that people may be substituting these oft-abused medicines with cannabis, according to Thomas Kerr, a researcher with the B.C. Centre for Excellence in HIV/AIDS.

"This isn't surprising and we're seeing the same effect all over the place measured in different ways," Dr. Kerr said. (Earlier this year, Dr. Kerr and his colleagues at the centre urged the Canadian medical establishment to embrace giving medical marijuana to pain patients instead of frequently abused opioids.)

The groups organizing hundreds of veterans in Atlantic Canada to take advantage of the country's most robust medical-marijuana coverage have long argued that the drug was replacing other – more harmful – pharmaceuticals such as opioids (for pain relief) and benzodiazepines (for anxiety and insomnia).

Benedikt Fischer, senior scientist at Toronto's Centre for Addiction and Mental Health, said pain and sleep issues are the most common reasons medical marijuana is prescribed.

"There's definitely overlap in the conditions and symptoms for which marijuana as well as opioids and benzos are being used," Dr. Fischer said.

Since 2008, the number of Canadians taking prescription sedatives – including benzodiazepines, but also sleep aids such as zopiclone – has remained steady at roughly 10 per cent, according to a bulletin issued last July by the the government-funded Canadian Centre on Substance Abuse. While illicit opioid use has skyrocketed in recent years, the number of Canadians prescribed to this class of heavy painkillers has dropped from about 21 per cent in 2008 to 15 per cent in 2013, according to that same bulletin, which provides the latest data available.

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Still, Dr. Fischer said newer data from the general population and a more rigorous analysis of the Veterans Affairs statistics is needed before any causality can be suggested.

A spokesperson for Veterans Affairs said in an e-mailed statement that this new "data does not allow the department to make any conclusions about the use of marijuana for medical purposes and the usage of other drugs."

Veterans Affairs Minister Kent Hehr declined a request for an interview on the subject last week, but he previously stated that he has accepted all of the Auditor-General's recommendations to create stricter controls on the program. Mr. Hehr has promised an update in the coming months to an ongoing internal review of medical-marijuana use among former soldiers.

Last fiscal year, 1,762 veterans used the only publicly funded plan in the country for medical marijuana. Groups that represent them offer a small, but lucrative, patient base for Canada's two dozen licensed producers, which are fighting for their share of a competitive market while facing pressure from an illegal dispensary sector that has spread east from Vancouver.

Mike Southwell, co-founder of the controversial New Brunswick-based Marijuana For Trauma (MFT) organization, said veterans who use his eight clinics say they much prefer cannabis to the pharmaceuticals.

"Most of them have been coming off of over 80 per cent of their [opioid and benzodiazepine] medications," said Mr. Southwell, a veteran who said he has dropped a handful of other drug prescriptions and now consumes about seven grams a day of cannabis to treat his post-traumatic stress disorder and back pain.

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On average, last year's marijuana prescriptions cost Veterans Affairs much more per patient ($11,656) than opioids ($316) or benzodiazepines ($73), according to government data.

Mr. Southwell said these costs are offset by former soldiers regaining their sex drive and ditching erectile dysfunction prescriptions – also covered by Ottawa – as well as a myriad of other benefits that come from using only medical cannabis.

"We've got testimonials rolling every day: 'I got my husband back.' 'I got my life back.' 'I'm able to feel again.' 'I'm able to love again.' I'm able to move again.' 'I'm able to sleep again,' " he said. "Those are amazing statements."

James Grant, a 79-year-old veteran living in a suburb of Charlottetown, said he has been able to get at least six hours of uninterrupted sleep and play a full 18 holes of golf since he got a prescription for cannabis capsules through a Marijuana For Trauma clinic a month ago.

He said his life has become immeasurably better since using cannabis because he no longer is "gobbling extra-strength Tylenols" to help fill gaps in his pain medication.

But he doesn't want to take the chance of regressing, so he said he will continue to take an opioid (a Butrans patch administering buprenorphine) for excruciating arthritis in his back and two benzodiazepine sleeping pills each night (Temazepam) so that he never wakes up to traumatic flashbacks.

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"The capsules are the thing for me," he said, adding that they have also helped his bowel movements become more regular. "I know what I have experienced before and I don't want to go down that road."