New medical cannabis guidelines for family doctors stress that they should authorize marijuana for only a small fraction of patients because many of its reported benefits have not been proved by rigorous clinical trials.
The guidelines, published Thursday in the Canadian Family Physician journal, warn that the number of randomized studies backing up the use of cannabis to fight various ailments is "extremely limited or entirely absent." The scientific evidence dictates that doctors should recommend the drug only when treating a handful of very specific medical conditions such as: chronic nerve pain, palliative cancer pain, muscle stiffness associated with multiple sclerosis or spinal cord injuries and the nausea and vomiting brought on by chemotherapy, according to Mike Allan, a professor of medicine at the University of Alberta and project lead for the guidelines.
Even then, patients should first consider synthetic cannabis pills and sprays now available at pharmacies before purchasing dried cannabis or oil products through Health Canada's mail-order system.
"We felt this was an area that was crying out for some guidance and assistance for front-line clinicians," said Dr. Allan, who added that patients' interest in the drug has been exploding as the legalization of recreational cannabis is expected this summer. "The biggest take-home message about the guidelines is: We have so little high-quality research, which is a real challenge."
The committee of nine medical professionals and one patient representative that drafted the guidelines found little to no acceptable clinical evidence that cannabis helps other conditions commonly cited by patients such as arthritis and anxiety or depression, said Dr. Allan, who also practises part time as a family physician in Edmonton. The guidelines also state that "common and consistent" side effects of using medical cannabis include drowsiness, dizziness and confusion.
The guidelines mirror a U.S. review of existing science published last year by the National Academies of Sciences, Engineering and Medicine that outlined nearly 100 conclusions about the benefits and harms of cannabis on a range of public health and safety issues. The federal panel's report stated that marijuana can almost certainly ease chronic pain and might help some people sleep, but it may also raise the risk of developing schizophrenia and trigger heart attacks.
It ended with a call for more scientific information about cannabis so that health-care professionals and policy makers can make sound decisions because the current lack of evidence "poses a public health risk."
Cannabis research has often been restricted because it has long been scheduled as an illegal narcotic and big pharmaceutical companies have not funded many trials because the plant cannot be patented like other medicines.
Mark Ware, a McGill University pain researcher and vice-chair of Canada's recent federal panel on marijuana legalization, said the new guidelines reiterate much of what is already known – or unknown – about cannabis and underscore the desperate need for more clinical trials.
"The sad truth is there haven't been many new studies in the last two or three years so all of these reviews are looking at the same body of data," Dr. Ware said. Last month, the federal government unveiled $1.4-million in total for 14 projects on a wide range of cannabis research aimed at helping Canadians understand the impact of the coming change to the country's drug laws.
Dr. Ware questioned the new guidelines' recommendation that doctors turn to pharmaceutical cannabinoids before authorizing patients to use cannabis, saying those medicines are often prescribed off-label despite a lack of evidence they work for many conditions.
"Because it's available in pharmacies, that makes it more acceptable to prescribe?"