Cannabis prescribed for pain linked with an elevated risk of heart problems

There may be a previously unreported risk of arrhythmias following medical cannabis use.


Chronic pain is a rising problem. Medical cannabis was approved in January 2018 on a trial basis in Denmark, meaning that physicians can prescribe it for chronic pain if all other measures, including opioids, have proven insufficient.

Medical cannabis comes in various formulations depending on tetrahydrocannabinol (THC) and cannabidiol (CBD) levels. Dronabinol (high THC), cannabinoid (more THC than CBD), and cannabidiol (high CBD) can be prescribed in Denmark. The drug can be inhaled, eaten, or sprayed in the mouth.

A new study determined the cardiovascular side effects of medical cannabis, and arrhythmias in particular, since heart rhythm disorders have previously been found in users of recreational cannabis. Scientists found that cannabis prescribed for chronic pain is associated with an elevated risk of heart rhythm disorders.

Between 2018 and 2021, 1.6 million Danish individuals received a diagnosis of chronic pain, according to the study. 4,931 patients (0.31%) reported receiving at least one cannabis prescription (dronabinol 29%, cannabinoids 46%, and cannabidiol 25%). Each user was matched to five chronically ill non-user controls by age, sex, and pain diagnosis. Following both groups for 180 days, the risks of developing new cardiovascular diseases were compared.

The average age of participants was 60 years. 63% among them were women. The study details the chronic pain situations of Danish medical cannabis users for the first time. 17.8% of patients had cancer, 17.1% had arthritis, 14.9% had back pain, 9.8% had neurological diseases, 4.4% had headaches, 3.0% had complicated fractures, and 33.1% had other diagnoses.

With a relative risk of 1.74, medical cannabis users had an absolute risk of new-onset arrhythmia of 0.86% compared to non-users, 0.49%. There was no difference in the risks of heart failure and new-onset acute coronary syndrome between the two groups. The outcomes were consistent across all types of medical cannabis and chronic pain conditions.

Dr. Nina Nouhravesh of Gentofte University Hospital, Denmark, said“Our study found that medical cannabis users had a 74% higher risk of heart rhythm disorders compared with non-users; however, the absolute risk difference was modest. It should be noted that a higher proportion of those in the cannabis group was taking other pain medications, namely non-steroidal anti-inflammatory drugs (NSAIDs), opioids, and anti-epileptics. We cannot rule out that this might explain the greater likelihood of arrhythmias.”

“Since medical cannabis is a relatively new drug for a large market of patients with chronic pain, it is important to investigate and report serious side effects. This study indicates that there may be a previously unreported risk of arrhythmias following medical cannabis use. Even though the absolute risk difference is small, patients and physicians should have as much information as possible when weighing up the pros and cons of any treatment.”

The research is presented at ESC Congress 2022.


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