A new scientific statement released by the American Heart Association this week is warning of potential negative cardiovascular dangers associated with using marijuana — as well as underscoring the need for randomized controlled studies of the drug.
The paper, published in the AHA’s journal Circulation on Wednesday, is a 22-page analysis of the existing research on marijuana consumption, which outlines both the risks and potential benefits of the drug. Dr. Martha Gulati, chief of cardiology for the University of Arizona College of Medicine and editor in chief of the American College of Cardiology’s website, CardioSmart.org, says it’s an important overview. “It’s not guidelines per se, but it’s a statement on what knowledge we have to date relating marijuana to cardiovascular health,” Gulati tells Yahoo Life. “Because we often do get asked this question in patients who have heart disease if it’s OK for them to use marijuana.”
To help unpack the paper’s main points, here’s what you need to know.
Marijuana use could increase the risk of arrhythmias and stroke
Throughout the study, the authors emphasize that conclusive evidence on how marijuana affects the heart is lacking. But they note that tetrahydrocannabinol (THC), the psychoactive ingredient in cannabis, may be dangerous for certain individuals. “[THC] stimulates the sympathetic nervous system while inhibiting the parasympathetic nervous system; increases heart rate, myocardial oxygen demand, supine blood pressure, and platelet activation; and is associated with endothelial dysfunction and oxidative stress.”
Part of the issue may be the way that THC stimulates the heart. “When people use marijuana, it can increase their heart rate,” says Gulati. “So it causes something called tachycardia, which is just a fast heart rate, but it also can make them at more risk of going into an arrhythmia [the heart beating too fast or too slow].”
She says this can be especially dangerous in those who consume marijuana frequently. “We know, especially with the THC component of marijuana, that it creates this fight-or-flight mechanism. So if I jumped out of a bush and scared you, you would kick in your fight-or-flight — your heart rate would go up; you would be scared. Your blood pressure would go up. That’s normal,” says Gulati. “Those are very protective mechanisms. But if you’re using a lot of marijuana throughout the day, you can sort of chronically be in that fight-or-flight state, and that’s not good for the heart.”
A 2020 post from Harvard Medical School adds that marijuana — likely due to the aforementioned effects — may increase the risk of heart attack and stroke as well. “The risk of heart attack is several times higher in the hour after smoking marijuana than it would be normally, research suggests,” Harvard writes. “And one survey suggests that smoking marijuana may raise the risk of a stroke.”
Despite marijuana’s risks, there are also many therapeutic effects
The authors make a point to clarify that while the drug may come with risks, there are many conditions for which it has shown to be an effective treatment. Among those listed are epilepsy, multiple sclerosis, wasting syndrome, opioid addiction, glaucoma, anxiety, depression, Crohn’s disease, hepatitis C, Huntington’s disease and Parkinson’s disease.
Interestingly, there is also research suggesting that some aspects of marijuana may actually benefit the heart. Cannabidiol (CBD), the nonpsychoactive ingredient in marijuana, has reportedly been shown to alleviate some symptoms of heart disease. CBD may reduce heart rate and blood pressure, as well as reduce inflammation, according to the authors of the AHA report.
Other studies have shown positive effects of the drug on the heart as well, including a retrospective study of more than 160,000 patients with heart failure that found that marijuana use “was associated with a lower risk of death while the patient was hospitalized.”
Paul Armentano, deputy director of the marijuana reform organization NORML, adds that one of the biggest longitudinal studies of long-term cardiovascular effects of cannabis, Coronary Risk Development in Young Adults (CARDIA), determined that neither lifetime nor recent use of marijuana was linked to a higher rate of cardiovascular disease.
“To date, the findings from these studies have categorically not identified cannabis use as an independent factor for increased risk of adverse cardiovascular events among otherwise healthy young/middle-age adults,” Armentano tells Yahoo Life, “including among those subjects who have inhaled cannabis for over two decades.”
Marijuana’s Schedule I classification makes it difficult to study
Although the authors of the AHA statement conclude that marijuana may be dangerous for those with heart disease, they also highlight evidence of the opposite, suggesting that it’s impossible at this stage to fully determine its safety. Gulati says this is due to its classification as a Schedule I substance by the Drug Enforcement Administration, which renders it impossible to study its effects on humans.
Robert Page II, chair of the writing group for the AHA’s statement and professor at the University of Colorado Skaggs School of Pharmacy and Pharmaceutical Sciences in Aurora, Colo., urges caution when interpreting the data. “With cannabis, we just don’t have the research and clinical data regarding potential cardiovascular benefits at this time. Unfortunately, we are limited to observational data that have suggested a risk for cardiovascular events,” Page tells Yahoo Life. “With that said, we desperately need research to address the risks but also possible benefits of cannabis use in the context of cardiovascular health.”
Page hopes that the statement can be used as a “tool” to inform both clinicians and patients on the full scope of data that does exist. But for now, Gulati says, she’ll continue to advise patients against taking cannabis. “Without the data … I don’t recommend my patients use marijuana,” she says.