Personal Health Navigator

Why medical marijuana may be better than opioids for treating cancer pain

Written by Paul Taylor

QUESTION: My father is 84 and has been diagnosed with terminal cancer.  The medication he has been prescribed for pain isn’t working. He wants to try medical marijuana. But getting a doctor to prescribe cannabis is like pulling teeth.  His doctor said there isn’t enough scientific evidence to support its use, even though it’s legally permitted by the Canadian government. What can I do to get my father cannabis?

ANSWER: Quite frankly, I’m surprised the doctor didn’t comply with your father’s wishes.

One of the main goals of medicine is to relieve suffering, explains Dr. David Juurlink, a drug-safety expert and head of Clinical Pharmacology and Toxicology at Sunnybrook Health Sciences Centre.

When the regularly prescribed drugs don’t provide adequate pain relief, a doctor should be willing to consider a patient’s request for medicinal cannabis, says Dr. Juurlink.

Of course, your father’s doctor may have raised a valid point that far more studies have been done on conventional prescription drugs than on the medical uses of marijuana.

However, recent interest in cannabis is now leading to a growing body of research that suggests it may help treat several cancer-related symptoms. Not only does it appear to ease pain in some patients, but cannabis might also alleviate the loss of appetite and nausea caused by chemotherapy cancer treatments.

“The stuff works,” insists Dr. Vincent Maida, a consultant in palliative medicine and wound management at the William Osler Health Centre in Toronto.

Dr. Maida, who has been looking after dying patients for more than two decades, considers himself to be an “early adopter” of medical cannabis.  He began conducting research studies on cannabis in the mid-1990s after some of his patients reported feeling better when they used recreational marijuana.

“No one has ever died directly of a marijuana overdose. Yet many people die every year from opioids,” which are the main compounds used in many prescription pain relievers, says Dr. Maida, who is also an associate professor at the University of Toronto.

Dr. Juurlink echoes his sentiments. “From a safety perspective, medicinal cannabis is miles ahead of many of the other drugs that sit on our pharmacy shelves.”

He says there is a small risk that some people may suffer from acute psychosis, particularly on high doses of some strains of cannabis. But, as a general rule, cannabis is safer than the opioid-based pain medications that are routinely prescribed to terminally ill patients.

Although opioids can provide much needed pain relief for dying patients, the drugs often cause unpleasant side effects such as severe constipation and sedation, says Dr. Juurlink.  “And very often they just don’t work that well.”

Many patients will develop tolerance to opioids with regular use. That means it takes a higher and higher dose to achieve the same effect.  At very high doses, “opioids can paradoxically make pain worse,” says Dr. Juurlink.  This intensification of pain is called opioid-induced hyperalgesia and it appears to result from the activity of these drugs on certain receptors in the brain that make patients hypersensitive to stimuli.

To make matters worse, prolonged use of an opioid leads to a physical dependence on the drug. Stopping the medication abruptly can trigger withdrawal symptoms such as diarrhea and abdominal pain. Patients must be gradually weaned off the drug – and that takes time and effort.

For all these reasons, it’s certainly worthwhile considering cannabis as an alternative to opioids for palliative-care patients.

Dr. Maida says it’s important for patients to know that medical cannabis is not the same as recreational marijuana.

Medical cannabis is produced by companies that are licensed and regulated by Health Canada. Doctors act as the gatekeepers by providing patients with an authorization to buy it.

The controlled cannabis products contain specific ratios of two medically-active compounds – tetrahydrocannabinol (THC) and cannabidol (CBD) which each have different effects on patients. The dried plant material is also free of pesticides, mold and other impurities.  The same cannot be said for recreational pot, which can differ widely in intensity and may contain contaminants.

Dr. Maida says it’s hard to predict if an individual patient will actually benefit from cannabis. “There is a lot of variation in response.”  He will often suggest that patients try two strains containing different levels of THC and CBD to see what might work. “The selection process involves a bit of trial and error.”

With this background in mind, let’s now return to your original question:  How does your father get access to medical cannabis?

Dr. Maida says your father should ask his doctor for a referral to another physician who is willing to authorize its use. “If a doctor doesn’t know the science behind prescribing medical marijuana, there are others who have that experience.”

He points out that the referral process is used in other situations where physicians may have a personal objection to a certain treatment.

Doctors are not required to personally carry out the wishes of their patients. But, in some cases, they have an ethical obligation to refer a patient to a physician who is willing to do so.

Medical cannabis certainly seems to be one of those cases where a referral makes sense. It is a legally available treatment that’s regulated by Health Canada.  What’s more, the available evidence suggests that it can provide symptom relief for some cancer patients.

Dr. Maida believes that medical cannabis will eventually become commonplace as further research is carried out and doctors learn more about its potential uses in health care.

For now though, patients seem to be the ones who are pushing for greater availability.

Dr. Juurlink says some of his patients have said they clearly benefited from cannabis. “If a patient says it is helping, or even if a patient has never tried it before but is failing with other therapies, I don’t see why a doctor wouldn’t consider a trial of cannabis.”


Photo by Flickr user Dank Depot – Creative Commons license

About the author


Paul Taylor

Paul Taylor, Sunnybrook’s Patient Navigation Advisor, provides advice and answers questions from patients and their families, relying heavily on medical and health experts. Email your questions to
and follow me on Twitter @epaultaylor

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