A new study suggests cannabis could be a safer and more effective substitute for opioids in the treatment of chronic pain, but can it help fight the opioid crisis?

Researchers at the University of British Columbia and the B.C. Centre on Substance Use conducted over 5,000 interviews with 1,152 people who used heroin and other drugs and reported chronic pain at some point from June 2014 to June 2017. 

The participants were largely from Vancouver's Downtown Eastside, and lead author M-J Milloy said the study aimed to discover "new interventions" that might "lower or address the risk of overdose" in heavy opioid users. 

More than 12,800 apparent opioid-related deaths occurred in Canada between January 2016, when the federal government started tracking the data, and March 2019, according to the latest available statistics from the Public Health Agency of Canada.

Milloy said chronic pain is one of the "driving factors" of the opioid crisis, adding that many who can't get effective pain relief can turn to the black market for opioids.

"This is the population that's really suffering the worst burden of mortality in the crisis," he said. "And there's been some work suggesting that cannabis might be beneficial in the overdose crisis. So we've really tried to use our data to figure out if that is true."

What they found was that daily cannabis use was associated with significantly lower odds of daily illicit opioid use, suggesting cannabis may serve as a substitute treatment in people with chronic pain. 

The story went viral online this week and was picked up in publications in Canada and overseas, including the Daily Mail and The Sun in the U.K.

What the articles failed to mention, however, is that Milloy is also UBC's inaugural Canopy Growth Professor of Cannabis Science. 

M-J Milloy was named inaugural professor of cannabis science at UBC last November. (Rafferty Baker/CBC)

While a spokesperson for the university says he receives no funding from any industry group, it is worth noting the cannabis company contributed $2.5 million to UBC and BCCSU for the professorship and research. 

Milloy said the fact that his study looked at daily cannabis use raised a "valid concern" about the risk of addiction, but added it's also linked to therapeutic benefits. 

"A lot of people who are benefiting from cannabis are the people who are using it every day," he said. 

"We are very aware of the risk of harms. And I want to emphasize that none of us think that cannabis is a panacea or a silver bullet to knock out the overdose crisis. What we do think, though, is that it has tremendous potential."

Conflicting research raises questions

A day after the UBC study was published, researchers at McMaster University published a review of almost 30 years' worth of data in the Canadian Medical Association Journal that examined the use of cannabis as a replacement drug for people with opioid addictions.

Researchers looked at six studies involving 3,676 participants dating back to 1991 in an effort to determine the effects of cannabis use on opioid addiction during methadone treatment.

What they found was starkly different than the UBC study — there is no consensus among studies that cannabis use is associated with reduced opioid use.

"There's a lot of hype and interest and hope that this could be a replacement. Could this be helping people with chronic pain or with opioid addiction?" said senior author Dr. Zainab Samaan, associate professor of psychiatry and behavioural neurosciences at McMaster.

"The reality is that there are no good studies or good evidence to show us it's beneficial."

The research also found cannabis use did not result in patients with opioid addiction staying in methadone treatment longer.

Challenges to cannabis research

Samaan concedes that studying the positive or negative effects of cannabis is difficult, especially when studying drug users with addictions to multiple drugs.

"When you've got a mix of drugs and a population who are already addicted to drugs, it's really hard to decipher," she said. "What is the benefit, what is the harm?" 

The McMaster study also concludes the overall quality of evidence was "very low," with "critical issues of inconsistency and imprecision to moderate risk of bias." 

"Even though it has been part of our society for decades, the study of this drug was hampered by its illicit label," said Dr. Hance Clarke, director of pain services at Toronto General Hospital.

"Many of the trials that the medical community are so desperately seeking are just about to be performed, and Canada has the opportunity to create the evidence that will decisively answer many of the unknowns," he said. 

"Unfortunately these reviews are only as good as the evidence being reviewed."

'Benefits for some'

Clarke uses cannabis as a treatment for chronic pain patients at the University Health Network Transitional Pain Service Clinic on an individual basis. 

"I have had patients that have completely stopped using opioids upon the introduction of cannabis, some have been able to reduce their daily opioid dose and remain on both often at lowered doses, others that have completely failed," he said. 

"The introduction of cannabis for individuals is neither risk-free nor a panacea, however in clinical practice there are benefits for some."

Clarke said more research on cannabis and opioid dependency is essential to get "credible data" for Canadians, and another review of poor quality research can't provide definitive answers.

"This is not the end of our journey to help Canadians," he said. "We remain at the doorstep."