Marijuana may be linked to heart problems — is it the smoke or THC that's harmful?

Americans are getting high in record numbers. As more people use marijuana, growing evidence suggests marijuana may be linked to certain heart problems. What’s not clear is whether the heart risks are from smoking marijuana or if it’s the THC in weed that could be harmful.

About 1 in 5 people over the age of 12, an estimated 61.9 people in the U.S. have used marijuana in the past year, up from 52.5 million the year before, according to the National Survey on Drug Use and Health data released on Nov. 13. As more states legalize recreational use, cannabis is easily the most popular mind-altering drug in the U.S.

It’s become so widely viewed as not harmful, a recent Pew Research poll found that 9 in 10 Americans believe marijuana should be legal for both medicinal and recreational use.

However, recent studies have found links between marijuana use and cardiovascular problems, including abnormal heart rhythms and even heart attacks. While some of the findings are contradictory — some find a risk of heart failure, others don’t — and no definitive conclusions can be made about marijuana’s risk to the heart, researchers say the signs shouldn’t be ignored.

Earlier this month the American Heart Association presented preliminary findings from two studies that found marijuana use was linked to a greater risk of both a heart attack and heart failure.

The results of the first study, which looked at people with a median age of 54, found a 34% increase in the risk of heart failure in people who used marijuana daily compared with those who had never used it.

In the second study, researchers analyzed patients who were in the hospital for any reason and found that people who used marijuana and had a medical condition like Type 2 diabetes had a significantly increased risk of heart attack, cardiac arrest or abnormal heart rhythm, compared to patients who didn’t use cannabis.

“I’m very worried,” said Robert Page, a clinical pharmacist who specializes in heart disease at the University of Colorado Skaggs School of Pharmacy. “It’s looking like cannabis may be a risk factor for developing cardiovascular disease.”

Dr. Peter Grinspoon, one of the leading cannabis researchers in the U.S., said that while it’s important to note the two studies do not directly prove marijuana causes heart problems, it’s an issue that needs to be urgently looked at.

“We absolutely need to research this much more extensively,” said Grinspoon, a primary care physician at Massachusetts General Hospital and an instructor at Harvard Medical School. “It’s critical that we figure this out.”

Is using marijuana bad for my heart?

Early findings from a large Danish study last year found that using medical marijuana for chronic pain was associated with a 64% increase in the risk of abnormal heart rhythms such as atrial fibrillation, which can raise the risk of stroke or death. The research didn’t show an increased risk of heart failure.

THC, the active ingredient in cannabis that gets people high, could be affecting the heart through its activation of the sympathetic nervous system, which is our body’s fight-or-flight response. That can trigger an increased heart rate and blood pressure, putting more strain on the heart.

“Anything that can raise your heart rate can cause heart attacks and potentially heart failure,” said Grinspoon.

Page, the lead author of a comprehensive statement on cannabis released by American Heart Association in 2020, wrote that cannabis may have some therapeutic benefits, but not for the heart.

“At this point, there are no cardiovascular benefits at all with any form of cannabis,” he said. “It’s just not there in my mind.”

Is it the smoke or the weed?

That’s where the science really gets murky. Because it can take years to conduct scientific research and evaluate the results, studies on cannabis are usually done on older forms of marijuana with far less potency than what is available today. The potency of cannabis — measured by how much THC is found in the product — has been rising for nearly half a century, increasing by about 0.29% every year from 1970 to 2017.

Although most studies have looked at people who smoke marijuana, more data is needed, Grinspoon said. His best guess is that it’s the smoke — which has the same type of carcinogens and tar that are in tobacco cigarettes — as opposed to the marijuana itself that may be affecting our hearts.

“It’s certainly not as bad as tobacco smoke, which kills 480,000 people a year,” said Grinspoon. “But cannabis smoke contains cyclic aromatic hydrocarbons, and these are things that there’s no way you could even argue that they’re OK for your heart.” Cyclic aromatic hydrocarbons are chemicals that result from burning tobacco, coal, oil, gas, wood and garbage that are damaging to DNA.

While vaping may mitigate some of the toxic chemicals of smoke, it’s not without risk, said Dr. Robert Kloner, a cardiologist and chief science officer at Huntington Medical Research Institutes in Pasadena, California.

“Vaping could be safer than smoking because you’re not inhaling the tars, you’re not going to be inhaling carbon monoxide associated with smoking,” he said.

Ultimately, what matters more is the dose consumed.

“If you take a puff once a week at a party, that’s not going to make a big difference to your heart,” Grinspoon said. “But if you’re puffing away on a vape pen, you know, 30 times a day, of course it is going to be bad for your heart.”

Are edibles safe?

Little is known about cannabis edibles such as gummies, chocolates, candies, brownies or beverages, Page said. While the number of children who have been poisoned from inadvertently consuming marijuana edibles has skyrocketed, there’s “very limited data” on what they do to the body, said Page.

It’s plausible that edibles are less risky because there’s no inhaled smoke. “If you can use a tincture or an edible, you don’t get any of the inhaled combustion products, which are particularly bad for your heart and can cause hardened arteries,” said Grinspoon.

Again, it’s about the dose.

“If you take half a gummy, or 2.5 milligrams, and fall asleep, it’s very unlikely you’re going to have coronary artery disease,” Grinspoon said.

Who is at risk?

People with coronary artery disease, hardening of the arteries or a family history of heart disease should be wary.

“If they had a heart attack six weeks ago, I wouldn’t start cannabis,” Grinspoon said. “I’d be very, very cautious unless there were incredibly compelling indications,” he added, referring to patients using it for medicinal purposes.

For someone with artery disease, if the heart starts beating faster and demands more oxygen as THC activates the fight-or-flight response, it could spell trouble.

“You’re getting kind of a double whammy,” he said. “That can lead to a heart attack.”

Even young people who may not know if they have high cholesterol or high blood pressure — conditions that put them at greater risk of heart disease — need to be careful.

“They think they’re invincible and [then] they use a cannabis product, and boom, they may have an event,” said Page.

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