Medical cannabis has a complementary role to play in fighting cancer pain, a study by researchers at the McGill University Health Centre (MUHC) has concluded.

It also found the use of cannabis would help reduce the total number of medications and opioids taken by patients.

After three months, Dr. Antonio Vigano's team said they saw "clinically significant reductions in pain scores in patients." These reductions persisted for a year, and the patients were able to gradually reduce their use of pain medication.

Nevertheless, Dr. Vigano said, "cannabis is not an alternative to pain treatments, it is a complementary treatment. "Cannabis has its own limitations, its own contraindications, so it's not miraculous," he said.

The researchers recruited 358 adult cancer patients for their study. The average age of the patients was 57, and about half of them were men. The most common cancer diagnoses were genitourinary and breast cancers, followed by bowel, lung and blood cancers.

Pain intensity, symptoms and total number of medications taken were analyzed. Daily morphine use was assessed at the time of the first medical cannabis prescription, and three, six, nine and 12 months later.

Overall pain severity and pain relief, as well as pain interference with daily life in the previous 24 hours, were also considered.

Statistically significant decreases were observed at three, six, and nine months when it came to the intensity of average and worst pain, overall pain severity, and how pain interfered with daily life.

Dr. Vigano said he began using medical cannabis in 2015, primarily to stimulate his patients' appetite. He realized over time that the substance also helped with pain control, possibly by relieving patients' stress and anxiety.

More than half of patients receiving cancer treatment and two-thirds of those with advanced, metastatic or terminal disease experience pain. Opioids are often prescribed, but relief is not always completely achieved.

"There are always patients who don't fully respond to conventional treatments or who have side effects," said Dr. Vigano. "So for these patients, we need to find something complementary to improve pain control and also quality of life."

Still, some patients are hesitant when it comes to adding medical cannabis to their treatment. It's a hesitancy that Dr. Vigano said he encounters more often in older patients, while younger ones are a little more familiar with the substance.

"The most important thing is to tell our patients that our goal is to control the symptoms, not to give a high," Dr. Vigano said with a laugh. "When there's a high, for us it's a side effect, so we always use the lowest effective dose."

The cannabis used usually comes in oil form (sometimes in capsules) or is administered in vapour form since inhaling smoke could be problematic for some patients.

The most effective cannabis products for pain relief appear to be those with a balance of the active ingredients tetrahydrocannabinol (THC) and cannabidiol (CBD), rather than a predominance of either.

The findings of the study were published in the medical journal BMJ Supportive & Palliative Care.

This report was first published in French by The Canadian Press on May 4, 2023.