Some Ontario doctors are hesitating to prescribe medical cannabis to patients suffering long-term pain, and a new McMaster University study shows it's because some still don't know how helpful or harmful it is.

That's despite medical cannabis being legal for 20 years.

"What we heard from the physicians we interviewed is they, by and large, feel ill-equipped ... because of limitations of training and the evidence out there," said Jason Busse, associate director of the Michael G. DeGroote Centre for Medicinal Cannabis Research at McMaster.

"The themes that came out of these interviews were not surprising."

Researchers conducted telephone interviews with 11 doctors between January and October 2019 and published their findings in the Canadian Medical Association Journal Open.

McMaster University says the study shows the main concerns among doctors surveyed included "potentially harmful effects on cognitive development, a possible worsening of existing mental illnesses in patients, and the drug's effects in older adults, which may include dizziness or drowsiness,"​

Despite the uncertainty, McMaster states the number of Canadians using medical cannabis has soared from just under 24,000 in June 2015 to 377,000 by September 2020.

The report says the "increased use of medical cannabis was likely the result of the easing of regulations, greater availability given the growing numbers of producers and cannabis clinics, and reduced stigma around the use of cannabis for therapeutic purposes."

But Busse said doctors need more proper guidance, saying medical cannabis products haven't undergone the same intense trials as other pharmaceutical drugs.

"I would hope almost all medications, if not all, are on the market because there has been empirical study, there has been evidence that is established that the benefits exceed the harm," he said.

"With medical cannabis, they typically don't have that kind of information."

Busse said the doctors interviewed normally refer patients to clinics that specialize in medical cannabis use.

"But at the same time, they expressed a lot of reservations as to whether these clinics were providing their patients with comprehensive information on benefits and harms and their perception was virtually any patient they would send ended up getting cannabis."

Busse said while it's easy to access medical cannabis, it's also difficult for researchers to study it.

"Health Canada has decided there's a much higher bar that needs to be met for research on these products than the bar required for patients to acquire and use them," he said.

"It's a real catch 22 situation in the sense that clinicians and patients want more evidence, but the current regulatory challenges are making it next to impossible to conduct the research in Canada that we need to answer those questions."