- New research indicates that chronic pain patients using medical cannabis are at a higher risk of heart arrhythmia than non-users.
- The Danish study noted a two-fold increase in the risk of arrhythmia, although the overall risk was still low.
- More research is needed to establish a link between cannabis and cardiovascular disease.
People who use medical cannabis for chronic pain are more likely to experience atrial fibrillation and other forms of heart arrhythmia compared to non-users.
Those are the findings of a study published this week in the European Heart Journal.
However, the authors noted that data on medical cannabis is still lacking due to legality issues, and more research is needed to support the findings.
Additionally, the authors also noted that the study did not address whether the risk is linked specifically to smoking cannabis, ingesting cannabis edibles, or a combination of both.
Another major limitation that the authors noted is that the study was not able to look at “disease severity, clinical measures, blood tests, and lifestyle factors,” all of which could contribute to an increased risk of heart issues independent of cannabis use.
Although the risk of arrhythmia among medical cannabis users was still low, it was statistically significant.
Researchers did not find any association between medical cannabis and acute coronary disease (ACS), an umbrella term that includes serious cardiovascular events like heart attack and unstable angina.
“There is very insufficient evidence related to medical cannabis and cardiovascular side-effects. Clinically, associations have previously been found with recreational cannabis use, but to our knowledge, this is the first study investigating associations with prescribed medical cannabis,” Dr. Anders Holt, MD, of Copenhagen University in Denmark, and author of the study told Healthline.
A Two-fold increase in arrhythmia risk
The study found that risk of new-onset arrhythmia, which included conditions like atrial fibrillation, flutter, and paroxysmal tachycardia, was doubled in those who used medical cannabis to manage chronic pain compared to a control group.
Holt and his team utilized health data from national Danish health registries to investigate the link between medical cannabis and arrhythmia. Medical cannabis is not formally approved for chronic pain management in Denmark, but a government program has allowed physicians to prescribe it for that reason.
Researchers looked at data from more than 1.8 million patients with chronic pain.
Out of that group, only a very small number of patients received medical cannabis: about 5,000 people.
The group of medical cannabis users were matched 1:5 with 27,000 patients that had similar characteristics, including age, sex, and use of other pain medications.
In large, population-based studies like this, it is impossible to remove all confounding factors, but the goal is to remove as many as possible.
Patients in the study did not have a history of arrhythmia, nor had they previously been prescribed medical cannabis.
Over a 180-day follow-up period, 42 patients who used medical cannabis developed an arrhythmia; in three out of four cases, it was atrial fibrillation.
Overall 0.8% of medical cannabis patients experienced an arrhythmia compared to 0.4% in the control group. The risk was greatest in patients with cancer and cardiometabolic conditions like diabetes.
No association was found between medical cannabis and acute coronary syndrome.
“These findings should spur further investigations into the viable use of cannabis treatment for chronic pain and particularly into possible side effects. It should be paramount to physicians that the ongoing legalization of cannabis meant for therapeutic use is kept purely scientific and not political,” said Holt.
Statistical versus clinical risk
Although the study demonstrates an increase in risk, questions remain about how this risk should factor into patient care.
“You need to distinguish statistical significance from clinical significance,” said Dr. Rod Passman, MD, a Professor of Medicine and Director of the Center for Arrhythmia Research at Northwestern University. Passman wasn’t affiliated with the study.
“If you tell someone their risk is double, that’s really important. But if you tell someone their risk goes from 0.4% to 0.8%, most of us would not believe that that is a major increase in risk that would impact clinical decision making like whether I would take a medication or not,” he said.
He notes that many pain medications, even over-the-counter nonsteroidal (NSAID) medications like ibuprofen, are associated with arrhythmia.
Opioids, pervasive and powerful pain medicines like morphine, codeine, and fentanyl, are too.
A 2018 review found that even at low doses could increase the risk of arrhythmia.
Patients and healthcare professionals will always need to assess risks and benefits when assessing treatment needs.
“I don’t think that I would take someone who was in chronic pain, which failed typical therapies, and prevent them from getting medical marijuana because of the potential risk of exacerbating their atrial fibrillation when that risk is going to be relatively low,” he said.
A dearth of data on medical cannabis
Both Passman and Holt acknowledge that good data on medical cannabis is sorely lacking. Prior research has tended to focus on recreational cannabis usage. With the rise of legalization in Europe and the United States, use of medical cannabis is steadily increasing.
“This is of increasing interest given the increasing use of cannabis, both for medical and recreational purposes…Often there’s a lot of problems with these studies because, historically, this has been an illegal medication. So we don’t have a lot of good, solid data on it,” said Passman.
“Prescribed medical treatment must be founded on sufficient evidence of effect, including considerable knowledge on side-effects which this study adds a sliver of, but more is certainly needed,” said Holt.
The American Heart Association has stated that there are “no cardiovascular benefits” to using cannabis, either recreationally or medicinally. In a scientific statement on cannabis and cardiovascular health issued in 2020, the AHA points out that in a variety of studies, cannabis consumption has been associated with atrial fibrillation and cardiovascular disease. They too, acknowledge a need for more and higher quality data and that there is “an urgent need for carefully designed, prospective short- and long-term studies.”
AHA spokesperson Robert L. Page II, PharmD, a Professor at the University of Colorado and Chair of the AHA’s 2020 scientific statement on cannabis, told Healthline that the Danish research “absolutely” aligns with the AHA’s statement.
“I treat cannabis use (particularly when vaped or smoked) as a potential risk factor for heart disease, which is why I do not recommend smoking or vaping any form of cannabis. Thus, medical providers should be screening for underlying cardiovascular risk factors or underlying conditions that could contribute to a heart attack, stroke or heart rhythm disturbance in anyone who uses cannabis,” he said.
The Bottom Line
A European study found that patients with chronic pain who used medical cannabis were more likely to experience heart arrhythmia than a control group.
While the risk of arrhythmia was still low (0.8%) among the medical cannabis group, it was a two-fold increase over the control group (0.4%).
Researchers and organizations, including the American Heart Association, say there is a tremendous need for more studies and high quality data on the association between cannabis and cardiovascular disease.
