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  • A new study finds that the risk for arrhythmia after cannabis use can increase.
  • However, the overall risk remains very low at under 1%.
  • Cannabis is increasingly being used to treat chronic pain.
  • Researchers say more study is needed.

People who use medical cannabis products for chronic pain may have a higher risk of heart rhythm disorders, or arrhythmias, according to preliminary results presented August 22 at the European Society of Cardiology scientific meeting in Spain.

“This study indicates that there may be a previously unreported risk of arrhythmias following medical cannabis use,” study author Dr. Nina Nouhravesh of Gentofte University Hospital in Denmark, said in a news release.

However, she said that even though there was a higher risk of arrhythmia among cannabis users, the absolute risk was “modest.”

In the study, researchers identified 1.6 million patients in Denmark diagnosed with chronic pain between 2018 and 2021. Over 4,900 of these patients picked up at least one prescription for a cannabis product (dronabinol, cannabidiol or other cannabinoids).

Dronabinol contains high amounts of THC, the main psychoactive compound in cannabis plants. Cannabidiol, or CBD, does not produce the same “high” as THC. Cannabis plants also contain other cannabinoids which have differing effects.

Researchers matched cannabis patients to similar patients — based on age, sex, and the type of chronic pain — who did not pick up a prescription for a cannabis product during the study period. They followed both groups for 180 days.

People who didn’t use medical cannabis had a small risk (0.49%) of being diagnosed with a new arrhythmia during the follow-up period.

For medical cannabis users, the risk was still small (0.86%), but it was 74% higher than for non-cannabis-users.

However, researchers pointed out that a greater proportion of people in the cannabis group were taking other pain medications such as nonsteroidal anti-inflammatory drugs (NSAIDs), opioids, and anti-epileptic drugs.

As a result, “we cannot rule out that this might explain the greater likelihood of arrhythmias [in the cannabis group],” Nouhravesh said in the release.

Dr. Nikhil Warrier, a cardiac electrophysiologist and medical director of electrophysiology at MemorialCare Heart & Vascular Institute at Orange Coast Medical Center in Fountain Valley, Calif., said the new study is consistent with other research showing a higher risk of arrhythmias in cannabis users compared to non-users.

One study he pointed to found that young adults with cannabis use disorder had a higher risk of being hospitalized for arrhythmia.

Another study found that cannabis users with existing health problems such as high blood pressure, high lipids or obesity were also at greater risk of arrhythmia-related hospitalization. The highest increase in these hospitalizations occurred among white males ages 45 to 54 years.

In addition, other research has found that young cannabis users with pre-existing depression have a higher risk of arrhythmia compared to cannabis users without depression.

However, Warrier pointed out that the Danish research is an “observational study, which inherently has its limits. So one should interpret the results with caution, as it may not imply causality.”

Likewise, Dr. Sherry Yafai, a cannabis expert and an emergency medicine physician at Providence Saint John’s Health Center in Santa Monica, Calif., said one of the limitations of the new study is that more people in the cannabis group were taking pain medications or anti-epileptic drugs than in the non-cannabis group.

She pointed to several studies showing that certain opioid pain medications and anti-epileptic drugs can increase the risk of arrhythmia.

As a result, Yafai said it is hard to know if the moderately higher risk of arrhythmias seen in the cannabis group is due to the cannabis products or to other medications that people were taking.

This, she said, also suggests that the two groups of patients were not perfectly matched.

While researchers did match cannabis and non-cannabis patients based on age, sex, and type of chronic pain, other factors may also influence the risk of arrhythmia.

“When somebody is taking more opiates, more anti-epileptics, and more NSAIDs, it often indicates that their disease prognosis is worse or their pain levels are much higher,” said Yafai.

This raises the following questions, she said: Did the cannabis group have a greater proportion of sicker patients?

If so, would those people have been more likely to develop arrhythmia due to their other health problems, even without cannabis use?

To answer these questions, additional research would be needed, with cannabis and non-cannabis groups matched by medication use, the severity of illness, and other factors.

While many people have used cannabis to find relief from chronic pain, Warrier said people should be aware that cannabis is not without side effects.

“I have had patients come to see me who are on cannabis for their chronic pain who don’t realize the full impact of this choice,” he said. So “it is important for them to recognize that this is not a risk-free endeavor.”

Yafai said it’s important for people to know that not all cannabis products are the same; each has different effects, as well as heart-related risks.

Products can contain THC, CBD, or other cannabinoids in varying combinations and amounts. Some products, such as vape pens, may contain higher amounts of THC than is naturally found in cannabis plants.

People who are older or who have underlying factors that increase their risk of arrhythmia should be especially cautious when using cannabis products to treat chronic pain.

“Like any medication that is ingested or inhaled, you really should consult with a cannabis specialist to decide if THC or other cannabinoids may be helpful and work best for you,” said Yafai.