With the advent of legalization, we are just starting to gain insight into the safety of marijuana use. Over the past decade, marijuana use, both recreational and medicinal, has grown as state governments across the U.S. have legalized its use. But while it might be legal for adults to light up, the question of whether it is harmful or helpful in many cases remains unanswered.
Researchers say the truth is complicated.
Though it has been studied for decades, much remains unknown about how marijuana, or cannabis, affects heart and brain health. And there are significant challenges to finding clear answers.
"The evidence that has been emerging from animal models show ramifications in the brain and in the heart, but the data for humans is more murky," said Dr. Fernando Daniel Testai, a neurologist at the University of Chicago Department of Neurology and Rehabilitation. Testai was lead author on an American Heart Association scientific statement last year that detailed what's known, and not known, about marijuana's effects on brain health.
In fact, new research published in the American Journal of Cardiology suggests that the potential impacts of marijuana use on arrhythmia risk are acute rather than long lasting, and that after extended periods of nonuse, the risks subside. Nevertheless, the research indicates there is an impact, although they did not find compelling evidence to suggest an increased risk of arrhythmias when assessing past use of marijuana.
“Marijuana is widely used across the United States, and marijuana use has increased from 2.4% in 2015 to 4.2% in 2018 among adults aged ≥65 years,” wrote first author Barbara N. Harding, PhD, with the Barcelona Institute of Global Health, and colleagues. “Marijuana use increases sympathetic nervous system activity and inhibits cardiac parasympathetic innervation, resulting in elevated heart rate, elevated blood pressure, and an increase in myocardial oxygen demand.”
Harding et al. tracked data from the Multi-Ethnic Study of Atherosclerosis (MESA), focusing on data from nearly 1,500 participants. All participants were between the ages of 45 and 84 years old and free of cardiovascular disease when they first enrolled in MESA from 2000 to 2002. After enrollment, follow-up examinations occurred every two to six years. Each individual underwent at least 24 hours of extended electrocardiographic (ECG) monitoring.
Marijuana users, whether they were still using it or had done so in the past, tended to be younger than individuals who had never used marijuana. They were also more likely to be men and/or have a history of smoking cigarettes.
Overall, older adults faced a “greater burden of atrial and ventricular arrhythmias” if they were current marijuana users. More frequent users, the authors explained, were linked to a greater risk of ventricular arrhythmias.
“We expected marijuana use close to the time of ECG monitoring to be the most relevant,” the authors wrote. “This was confirmed in our results, with point estimates increased among the majority of associations with current marijuana smokers, whereas the same was not true for past users. These findings may reflect acute changes in arrhythmia risk occurring after marijuana use.”
The authors noted that they “did not find compelling evidence to suggest an increased risk of arrhythmias when assessing past use of marijuana.” This could mean the risks linked to marijuana use subside over time, but there were also signs in the research that pointed to premature ventricular contractions among past users.
Though the team hoped to learn more about the relationship between marijuana use and atrial fibrillation, the study’s sample power “was not adequate enough.”