The College of Family Physicians is issuing guidelines to Canada's 30,000 primary-care doctors about which patients should and should not get prescriptions for medical marijuana.

The organization says there is no evidence supporting the use of cannabis for low back pain or fibromyalgia, but it can be considered for nerve-damage pain caused by such conditions as metastatic cancer, shingles and injury.

Even with neuropathic pain, doctors should consider using medical pot only after trying standard medications and therapies, the College of Family Physicians says. (Darryl Dyck/Canadian Press)

College CEO Dr. Francine Lemire said the lack of research into cannabis has left many family doctors unsure about which patients could benefit from medical-grade weed and what dose should be prescribed.

"We're aware that there is demand out there by patients for dried cannabis for medical purposes," Lemire said Monday from Ottawa. "We're aware of the relative lack of evidence, good solid evidence, for when to authorize or not to authorize [its use].

"And we felt that it was important for us to share what evidence there is with physicians and to support them in how to prescribe."

The college's recommendations, which are spelled out on the organization's website, say there is no research evidence supporting the use of cannabis for low back pain or fibromyalgia, but it could be considered for nerve-damage pain caused by such conditions as multiple sclerosis, metastatic cancer, shingles, diabetic neuropathy and severe injury.

But even in the case of such pain-causing conditions, doctors should consider using medical pot only after trying standard medications and therapies, including pharmaceutical cannabinoids, the document says.

"Authorizations for dried cannabis should only be considered for patients with neuropathic pain that has failed to respond to standard treatments."

Before prescribing, the college advises doctors to conduct a pain assessment, assess patients for anxiety and mood disorders, and screen them for existing substance use disorders.

The guidelines say patients under 25, those with substance abuse, cardiovascular or respiratory disease, and women who are pregnant, planning to become pregnant or breastfeeding should not be prescribed medical marijuana.

When its use is considered appropriate, the family doctor should regularly monitor the patient's response to treatment and discontinue authorization for its use if the smokable herb is clearly ineffective or causing harm, the college said.

In April, Health Canada changed its regulations to put prescribing of therapeutic marijuana in the hands of physicians, while supply of the dried herb was handed over solely to licensed growers for distribution to patients. Previously, patients with proven medical need had been allowed to grow or buy cannabis for personal use.

The shift in regulations put doctors across the country in an unenviable position: the onus for authorizing the use of medical pot was now their responsibility, yet many knew little about which conditions might be helped by the herb, what dose was appropriate and when it shouldn't be given to a particular patient, Lemire conceded.

"We realize they have been placed in a difficult situation, that the conditions that many patients present with when they're requesting marijuana are often complex, that the evidence to prescribe medical marijuana is often lacking," said Lemire, stressing that it's critical that more research into pot's safety and effectiveness for various diseases be conducted.

"We feel that it's important for physicians not to authorize marijuana for medical purposes just because a patient is requesting it," she said. "So there really is a need to review the condition of the patient, look at therapeutic approaches that have been used in the past and … to be better informed about the evidence that is or isn't there in relation to marijuana prescribing."