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Researchers are learning how THC in cannabis may affect the heart.
  • THC is the main mind-altering (psychoactive) ingredient in cannabis, or marijuana, that can cause a person to feel high.
  • THC-containing products stimulate the heart as well as promote vascular inflammation and oxidative stress.
  • This may lead to elevated blood pressure, abnormal heart rhythms, and overall higher risk of heart attack, stroke, and sudden death.

Cannabis may have medicinal properties, but it could also be harmful to the heart and blood vessels, according to a report from the American Heart Association (AHA).

The AHA’s statement in the journal Circulation looked at several studies on the topic, as cannabis use has increased over the past decade.

Cannabis, also known as marijuana, refers to the varieties of cannabis plants that contain tetrahydrocannabinol (THC).

THC is the main mind-altering (psychoactive) ingredient in cannabis that can cause a person to feel high. Cannabinoids are compounds in cannabis. Cannabidoil or CBD is a commonly known cannabinoid said to have some health benefits. CBD is different from THC.

Researchers have had a tough time trying to study cannabis, as it is listed by the U.S. Controlled Substances Act as a Schedule 1 controlled substance. By definition that means it does not have a medical use and is likely to be misused. In the report, the AHA encouraged the federal Drug Enforcement Administration to remove it from the designation.

Chemicals in cannabis have been linked to higher risk for heart attack, heart failure, and atrial fibrillation. But those studies are observational and did not prove that the chemicals were the cause for the increased risk.

One study cited in the AHA statement reported that 6 percent of patients under the age of 50 who had a heart attack used cannabis. It was linked to having worse all-cause and cardiovascular mortality. Another study noted a significantly higher chance of having a stroke in cannabis users ages 18 to 44, with even greater odds in those who consumed it more frequently compared to those who did not use cannabis.

Dr. Chip Lavie, a cardiologist at the Ochsner Medical Center in New Orleans, Louisiana, said it’s already known that cannabis can have adverse effects on coagulation, increase acute cardiovascular events, and lead to poor vascular effects.

“We still do not have a feel on the impact on occasional users, high dose users, and very chronic users,” Lavie told Healthline.

When cannabis is used on a short-term basis in some patients, the benefits may outweigh the risks. Additional dangers with impure products and vaping still exist, though, he noted.

Dr. Muthiah Vaduganathan, a cardiologist at Brigham and Women’s Hospital in Boston, Massachusetts, pointed out that certain forms of cannabis delivery, such as vaping, can have unique cardiovascular health implications.

Because cannabinoid receptors are distributed all over the body, including in the heart, there’s a potential impact for effects on the heart, Vaduganathan said.

Not all the research on cannabis shows harm, the AHA report stated.

THC-containing products stimulate the heart as well as promote vascular inflammation and oxidative stress. This may lead to elevated blood pressure, abnormal heart rhythms, and overall higher risk of heart attack, stroke, and sudden death, explained Dr. Michael Miller, a cardiology professor at University of Maryland School of Medicine.

If THC concentrations are too high, or taken in a short amount of time, there’s the potential for it to create adverse reactions such as in older people on existing medications.

In contrast, CBD-containing products reduce inflammation and emotional stress that in turn, may serve to reduce the risk heart disease.

“I was not aware of the potential opposing effects between THC in the promotion of heart disease as compared to CBD which may protect against its development and progression,” Miller noted.

Although cannabis can be an effective treatment for medical purposes such as seizure control, or reducing nausea and improving appetite in people with cancer or HIV, some people aren’t aware of its potential harms when used for recreational or nonproven purposes, Miller said.

Miller hopes to see a well-designed clinical trial to determine whether daily use of CBD reduces the risk of a heart attack, stroke, or cardiovascular death.

Experts cite a lack of robust data in specifying the harms and benefits of cannabis on the cardiovascular system. Due to rising concentrations of THC in cannabis, earlier studies may only reflect the impacts of lower levels of THC on people, the AHA report stated.

Most cannabis studies are observational and don’t take into account that some cannabis users also smoke cigarettes, Miller added.

“I would love to know whether, and to what extent, THC may be harmful to the heart in the absence of major risk factors such as cigarette smoking,” he added.

Dr. Stephen Sidney, a senior research scientist with the Kaiser Permanente Northern California Division of Research in Oakland, California, said more research is urgent, as more people 65 and older are using cannabis — and they are at the highest risk for heart attack.

“Most of what we know about the cardiovascular effects of marijuana comes from studies of smoked marijuana. Much more research needs to done on other forms of marijuana, such as edibles, tinctures, and topic preparations,” Sidney told Healthline. “We also need to study how marijuana vaping affects the heart and lungs, because this has overtaken smoking of marijuana cigarettes as the most common use by teens.”

Patients and doctors need to be open about cannabis use and implications, Vaduganathan said.

“While cardiologists often ask and counsel patients about tobacco use, they infrequently screen for cannabis use. Patients similarly may not recognize that cannabis can have important effects on blood pressure, cardiovascular drug metabolism, and overall heart health — some of these may actually be very similar to the adverse health effects of tobacco smoking,” Vaduganathan said.

Some forms of cannabis use are allowed in 47 states, the District of Columbia, and 4 out of 5 U.S. territories. Selling it and using it is still illegal federally, although varying procurement and usage practices are legal in many states.