Patients with chronic pain who used cannabis daily for one year did not have an increase in serious adverse events compared to pain patients who did not use cannabis, according to a new study.

“This is the first and largest study of the long term safety of medical cannabis use by patients suffering from chronic pain ever conducted,” says lead author Mark Ware, associate professor of family medicine and anesthesia at McGill University.

“We found that medical cannabis, when used by patients who are experienced users, and as part of a monitored treatment program for chronic pain over one year, appears to have a reasonable safety profile.”

medical cannabis

Published in the Journal of Pain, the study is part of the Cannabis for the Management of Pain: Assessment of Safety Study (COMPASS), that started in 2004. Researchers followed 215 adult patients, with chronic non-cancer pain, who used medical cannabis, and compared them to a control group of 216 chronic pain sufferers who were not cannabis users.

The cannabis users were given access to herbal cannabis containing 12.5 per cent THC from a licensed cannabis producer. Cannabis was dispensed through the hospital pharmacy at each site, and patients collected their supply every month after completing the necessary visits and tests.

Along with information on adverse effects, subjects underwent lung function and cognitive testing, and were asked about their pain, mood, and quality of life over the one year of follow up. Several of the participants underwent complete panels of blood tests for routine biochemistry, liver, and kidney function, and selected hormone levels. The average amount of cannabis used overall was 2.5 grams per day whether smoked, vaporized, or taken as edibles.

“Our data show that daily cannabis users had no greater risk than non-users (control group) to experience serious adverse events, says Aline Boulanger, director of the pain clinic at the Centre hospitalier de l’Université de Montréal. ‘’We found no evidence of harmful effects on cognitive function, or blood tests among cannabis consumers, and we observed a significant improvement in their levels of pain, symptom distress, mood, and quality of life compared to controls.”

The researchers did report an increased risk of non-serious adverse events in medical cannabis consumers, including headache, nausea, dizziness, somnolence, and respiratory problems associated with smoking.

“It is important to note the limitations of the study,” Ware says. “Patients were self-selected, not randomized, and most were experienced users. So what we are seeing is that it appears to be a relatively safe drug when used by people who have already determined that it helps them. We cannot draw conclusions about safety issues of new cannabis users.”


This text is published here under a Creative Commons License.
Author: Julie Robert-McGill University
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