WEDNESDAY, May 3, 2023 (HealthDay News) -- Medical marijuana can safely reduce cancer pain, and is apparently so effective that patients wind up taking lower amounts of opioids and other pain meds, a new study reports.

Weed produced clinically significant reductions in cancer patients’ worst pain, average pain and overall pain severity, said senior researcher Dr. Antonio Vigano, an associate professor of oncology and medicine at McGill University Health Center in Montreal.

“Medical cannabis can be safely introduced in the care of cancer patients and can really lead to a decrease in different parameters by which we measure cancer-related pain,” Vigano said. “These reductions in those measures can be stable and can last up to one year of follow-up.”

Adding cannabis to a patient’s pain regimen also caused as much as a 32% decrease in the use of opioids and other pain medications, according to the study.

“As a consequence of using pot, we could also see a reduction in overall consumption of medication,” Vigano said. These reductions included opioids, antidepressants, anti-convulsives and non-steroidal anti-inflammatory drugs (NSAIDs).

Up to now, medical cannabis has largely been seen as a way to treat nausea and vomiting caused by chemotherapy, researchers said in background notes. Two marijuana-derived drugs, dronabinol and nabilone, have been approved for that use.

For this study, Vigano and his colleagues tracked for up to one year 358 adults with cancer whose treatment data was submitted to the Quebec Cannabis Registry between May 2015 and October 2018.

The patients’ average age was 57, and the most common cancer diagnoses were genital and urinary, breast and colon.

Pain was the most frequently reported symptom that prompted a prescription for medical cannabis, with 72% of cases citing it, researchers found.

Most patients took their medical cannabis by mouth (57%), through oils or capsules, Vigano said. About 13% smoked or inhaled their weed, and 25% combined one or more modes of administration.

Patients entered the study with their worst pain around 5.5 on a scale of 1 to 10, Vigano said.

At nine months, patients using weed had a 35% decrease in their worst levels of pain and a 43% decrease in the amount that cancer pain interfered with their daily lives.

After a year, patients also had a 33% decrease in their average pain and a 32% decrease in their overall pain severity.

These were clinically significant decreases, strong enough that they cannot be considered a “placebo effect,” Vigano said.

However, the effects of medical marijuana tended to wane over time, as did pot's ability to reduce a patient’s need for other pain medications, researchers found.

For example, the use of opioids had been cut by 31% at the six-month mark, but by nine months it was only down 14% compared to the start of the study.

These effects likely wane because pain increases as cancer worsens, Vigano said.

“At six months, probably you can observe the maximum effect of medical cannabis before the disease progresses and the gains that were established previously are lost a bit,” Vigano said.

What worked best

The most effective products for pain relief contained a balanced blend of THC, the chemical in pot that causes intoxication, and cannabidiol (CBD). CBD doesn’t cause intoxication, and a prescription CBD oil called Epidiolex has been approved to treat epilepsy.

Products with a balanced THC/CBD blend reduced a greater number of pain measures than THC-dominant or CBD-dominant products, researchers said.

The two most common side effects of medical pot were sleepiness, reported by three patients, and fatigue, reported by two, researchers said.

“Only five patients had to stop medical cannabis because of side effects,” Vigano said. “All the adverse side effects were actually managed by decreasing the dose and adjusting or changing the product.”

Vigano thinks that cannabis probably helps patients cope with their pain more than it causes an actual decrease in pain intensity.

“It's really the ability of dissociating the patient from his pain experience,” Vigano said. “A patient will commonly tell me the pain is still there, but I can live with it. And that is really what medical cannabis will be able to provide. They better cope with this source of physical suffering.”

The findings were published May 2 in the journal BMJ Supportive & Palliative Care.

The new study “reinforces what I see clinically in my own practice,” said Dr. Raja Flores, chair of thoracic surgery for the Mount Sinai Health System in New York City.

“I prescribe medical marijuana and I found it helpful, especially in patients with advanced disease on a ton of other medications,” Flores said. “It really seems to cut down the amount of pain and opioid medications that they use, which in turn then lets them feel better, make them less constipated. It increases their appetite, it elevates their mood a little bit.”

However, Flores emphasized that medical – not recreational – marijuana products are what have proven helpful in his practice, and particularly for certain cancer patients.

“It has to be the right patient. Not just any person who has cancer -- it has to be a person who is really being incapacitated not only by cancer, but by the medications, by the opioids, painkillers, anti-nausea medication,” Flores said. “Frequently, when patients have intractable cancer, it’s not just the cancer, but it’s everything that we’re giving them that has a lot of side effects. And if the medical marijuana can decrease the amount of medication they’re on, I think that’s a good thing."

Despite these findings, Vigano said weed should still be considered only one tool in the pain-control arsenal, not a substitute.

“My definition of medical cannabis is a complementary treatment which in certain patients can be effective and can lead to a reduction in medication,” Vigano said. “But medical cannabis has to be a complementary, not an alternative, option.”

There might be situations “where it’s the only option available because of the poor tolerability of patients to conventional medications,” Vigano added. “But this, I would say, is more the exception than the rule.”

Vigano added that marijuana used in health care settings like cancer treatment needs to be handled by doctors, to ensure proper dosages of effective products.

“Medical cannabis needs to be supervised by health professionals. It cannot be left in the hands of patients to decide what to do or in the hands of people who are dealing with cannabis which is not sold for medical purpose, but is sold for recreational purposes,” Vigano said.

In response to this study, the American Cancer Society said it “supports the need for more scientific research on cannabinoids for cancer patients, and recognizes the need for better and more effective therapies that can overcome the often debilitating side effects of cancer and its treatment.”

“The Society also believes that the classification of marijuana as a Schedule I controlled substance by the U.S. Drug Enforcement Administration imposes numerous conditions on researchers and deters scientific study of cannabinoids,” the society said in its statement. “Federal officials should examine options consistent with federal law for enabling more scientific study on marijuana.”

More information

The American Cancer Society has more on marijuana and cancer.

SOURCES: Antonio Vigano, MD, associate professor, oncology and medicine, McGill University Health Center, Montreal, Quebec, Canada; Raja Flores, MD, chair, thoracic surgery, Mount Sinai Health System, New York City; BMJ Supportive & Palliative Care, May 2, 2023; statement, American Cancer Society