Marijuana may harm heart, experts say

By Dennis Thompson, HealthDay News
THC, the chemical behind marijuana's "high," interacts with receptors that activate a person's sympathetic nervous system, researchers say. Photo by lovingimages/Pixabay link back to: 
THC, the chemical behind marijuana's "high," interacts with receptors that activate a person's sympathetic nervous system, researchers say. Photo by lovingimages/Pixabay link back to: 

As marijuana use becomes more common, could heart troubles follow?

Yes, warns a new statement from the American Heart Association (AHA).


A full understanding of how marijuana affects the heart and blood vessels remains limited by a lack of adequate research, but some chemicals in cannabis -- particularly THC, the chemical behind marijuana's "high" -- have been linked to an increased risk of heart attacks, heart failure and atrial fibrillation, the statement says.

Marijuana is "just like any other medication," said statement author Robert Page, a professor of clinical pharmacy at the University of Colorado Skaggs School of Pharmacy and Pharmaceutical Sciences, in Aurora. "Medications have side effects, and some of those side effects can be cardiovascular, and we're still trying to figure that out with cannabis."

Page and his colleagues on several AHA councils and committees scoured the medical literature for evidence regarding the effects of marijuana on the heart.


They came away concerned that marijuana can affect the body in ways that could harm heart health.

THC in particular interacts with receptors that activate a person's sympathetic nervous system, Page said.

"That's your 'fight-or-flight' response," Page explained. As a result, your heart could start beating rapidly or irregularly, your blood vessels could constrict, or your blood pressure could skyrocket -- all conditions that increase risk of heart attack and stroke.

The way marijuana is consumed might also increase stress on the heart. Smoking pot has been shown to increase blood concentrations of carbon monoxide fivefold, and carbon monoxide has been associated with heart problems like chest pain, heart attacks and abnormal heart rhythms.

Pot smokers also experience a threefold increase in tar, which is inhaled through partly burnt plant matter, according to the report.

On the other hand, the other major marijuana chemical, cannabidiol (CBD), appears to slow heart rate, lower blood pressure, relax the arteries and potentially reduce inflammation -- all things that are potentially good for heart health.

But until there is better data on risks versus benefits, "we definitely do not recommend that people use marijuana," said Dr. Johanna Contreras, director of the division of heart failure at Mount Sinai St. Luke's and Mount Sinai West, in New York City.


Paul Armentano is deputy director of the marijuana advocacy group NORML, in Washington, D.C. "It has long been understood that cannabinoids can have varying effects on the cardiovascular system. That is why NORML has consistently cautioned: Patients with a history of cardiovascular disorders, heart disease or stroke may also be at an elevated risk of experiencing adverse side effects from marijuana, particularly smoked cannabis," he explained.

"That said, however, longitudinal studies assessing cannabis use long-term in otherwise healthy subjects have generally failed to show evidence that those who consume cannabis are at any greater risk of suffering from adverse cardiovascular events than are those who abstain from it," Armentano added.

Regardless, the AHA experts called on the U.S. federal government to remove marijuana from its Schedule 1 drug list so that it can be widely studied by scientists.

The report noted that 47 U.S. states now allow some form of cannabis use, making the federal ban on marijuana an unnecessary obstacle to research efforts.

Page said, "We've seen a huge uptick, particularly during the COVID crisis, of young adults using cannabis. We don't have a lot of great data about the long-term impact cannabis can have. From a health policy consideration, we really need to have studies both short-term and long-term to evaluate cannabis use."


The U.S. government also should increase research funding regarding marijuana use, and the U.S. Food and Drug Administration should step in to create standardized labeling about the amount of THC and CBD contained in all legal cannabis products for sale, he said.

Levels of these chemicals can vary widely between marijuana products, Page noted.

"With the advent of dispensaries, realize that this isn't your grandfather's marijuana," Page said. "THC content is exceedingly higher in the products you may be getting from a dispensary."

Page also stressed that patients need to be transparent with their health care providers in regards to use, so any potential health problems or drug interactions can be avoided.

The AHA statement was published online Aug. 5 in the journal Circulation.

More information

The U.S. Centers for Disease Control and Prevention has more about the health effects of marijuana.

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