cannabis and heart rate

Pot Use Appears to Change Structure of Your Heart

By Dennis Thompson
HealthDay Reporter

FRIDAY, Dec. 20, 2019 (HealthDay News) — Regular pot use might potentially cause changes in the heart’s structure, a new study suggests.

People who regularly use marijuana tend to have a larger left ventricle, which is the main pumping chamber of the heart, according to the findings.

Routine stoners also appeared to have early signs of impaired heart function, measured by how the fibers of the heart muscle deform during contraction, the British researchers said.

But the heart appears to recover in both size and function once a person stops using marijuana, the study found.

“Those who used cannabis regularly had enlargement of the heart, but when they saw the patient had stopped using the drug, it seems the function was improved,” said Dr. Mary Ann McLaughlin, a cardiologist at Mount Sinai Hospital in New York City who reviewed the findings.

The researchers warn that the study “should be interpreted with caution, and more research is required to understand the potential mechanisms and dose-related effects of cannabis use.

But the results jibe with concerns people have had about the effects of pot on the heart, said Dr. Martha Gulati, editor-in-chief of the American College of Cardiology’s patient education website,

“There’s so much we don’t know about cannabis use and its effect on the heart, but one of the things we do know is that when people use marijuana, particularly if they smoke it, the heart rate and the blood pressure go up, and the heart has to work harder,” Gulati said.

The study, led by Dr. Mohammed Khanji, from Queen Mary University of London, involved more than 3,400 people in the United Kingdom, of whom 47 were current regular users of marijuana and 105 were previously regular users. The rest rarely used pot, if at all.

Khanji and his team studied MRIs to assess both the structure and function of participants’ hearts.

Although the size of the left ventricle was larger in regular pot users, the other three chambers of the heart remained unaffected, researchers added. The heart also appeared to pump the same amount of blood, regardless of marijuana use.


The findings were published Dec. 18 in JACC Cardiovascular Imaging.

McLaughlin characterized the study as “hypothesis-generating,” rather than a solid result.

“It’s not a definitive answer by any means, but it gives us reason to investigate the effect of marijuana on heart structure,” she said.

Because the study was observational, it’s hard to know whether other factors might have caused the heart structure changes associated with marijuana use, McLaughlin said.

“Alcohol can also cause similar types of changes in the left ventricle with chronic drinking, which can get better when people stop drinking,” she said. “They said they adjusted for alcohol use in this study, but the question is whether the use was adequately assessed.”

Europeans also are known to mix their marijuana with tobacco, which has notoriously harmful effects on the heart, said Paul Armentano, deputy director of NORML, a group advocating reform of U.S. marijuana laws.

Experts also noted that the number of pot users in this study was very small.

“Replications with more extensive measures and a dramatically larger sample of cannabis users do seem quite justified,” said Mitch Earleywine, a professor of psychology at the University at Albany-State University of New York and a NORML advisory board member.

If marijuana is indeed the cause, it’s hard to say what exactly about pot is affecting the heart, physicians say.

It could be the smoke that’s being inhaled that places strain on the heart, or it could be THC, the chemical in pot that gets you high, said Dr. Larry Allen, a professor of cardiology at the University of Colorado School of Medicine in Aurora.

THC has been shown to increase heart rate and blood pressure, cause blood to clot more easily, and affect the inner lining of blood vessels, he said.

“We have some basic laboratory data that suggests there may be adverse health effects of THC,” Allen said.

Until there are more answers, people with heart problems might want to avoid pot, the experts said.

“If you have heart disease, you should really use marijuana with caution,” Gulati said. “In fact, I, as a cardiologist, would recommend you not to use it because of the physiologic effects of increasing your heart rate and putting more demand and stress on the heart.”

People who regularly use marijuana tend to have a larger left ventricle, which is the main pumping chamber of the heart, according to the findings.

Marijuana and heart health: What you need to know

Access to marijuana is growing, but marijuana benefits and its risks have not been carefully studied.

Image: © UrosPoteko/Thinkstock

In many states in this country, you can legally use marijuana for a range of health benefits, including the treatment of chronic pain, anxiety, and nausea. Smoking is the fastest way to feel the effects of marijuana, which is derived from the Cannabis sativa plant. Yet marijuana smoke contains many of the same toxins, irritants, and carcinogens found in cigarette smoke — a known contributor to heart disease as well as cancer.

Marijuana cultivation and use dates back some 6,000 years. However, the cardiovascular and other health effects of cannabis aren’t well studied. That’s partly because under federal law, cannabis is a Schedule I substance, meaning it has “no currently accepted medical use and a high potential for abuse.” That designation places numerous restrictions on researchers, making it difficult to carry out rigorous research on marijuana.

“As a result, everything we’re told about what marijuana does or doesn’t do should be viewed with a certain amount of caution. This holds equally true for the risks as well as the benefits,” says Dr. Kenneth Mukamal, associate professor of medicine at Harvard-affiliated Beth Israel Deaconess Medical Center.

Pot and pain

Some of the strongest evidence supporting the medical use of marijuana is marijuana’s benefits for managing chronic pain. Cannabinoid compounds (see “Cannabis 101”) interact with receptors in nerve cells to slow down pain impulses and ease discomfort. Cannabinoids also have been shown to be effective in quelling nausea and vomiting. In addition, marijuana is a powerful appetite inducer. The combination of these attributes makes marijuana a therapeutic option for people coping with the side effects of chemotherapy and others who are in danger of unintended weight loss. However, in conditions where gaining extra weight might exacerbate existing health problems, such as diabetes, appetite stimulation would be counterproductive.

Cardiovascular effects

One of the few things scientists know for sure about marijuana and cardiovascular health is that people with established heart disease who are under stress develop chest pain more quickly if they have been smoking marijuana than they would have otherwise. This is because of complex effects cannabinoids have on the cardiovascular system, including raising resting heart rate, dilating blood vessels, and making the heart pump harder. Research suggests that the risk of heart attack is several times higher in the hour after smoking marijuana than it would be normally. While this does not pose a significant threat to people who have minimal cardiovascular risk, it should be a red flag for anyone with a history of heart disease. Although the evidence is weaker, there are also links to a higher risk of atrial fibrillation or ischemic stroke immediately following marijuana use. Consistent with these links, studies by Dr. Mukamal and colleagues also suggest that marijuana smoking may increase the long-term death rate among heart attack survivors.

Questions remain on marijuana’s benefits and risks

Most of the evidence linking marijuana to heart attack and stroke is based on reports from people who smoked it. So it’s hard to separate the effects of cannabinoid compounds on the cardiovascular system from the hazards posed by the irritants and carcinogens contained in the smoke. Because cannabis smoke is known to cause airway inflammation, wheezing, and chest tightness, people with lung diseases should not smoke it. Other people who should just say no to marijuana include those who may be vulnerable to developing schizophrenia or addiction.

Cannabis 101

The cannabis plant contains more than 100 unique chemical components classified as cannabinoids. These are the active ingredients that bind to specific receptors in the brain and other parts of the body. The two most prevalent types are tetrahydrocannabinol (THC), which is primarily responsible for the mind-altering properties sought out by recreational users, and cannabidiol (CBD), which has no psychoactive effect. Cannabidiol may actually work to offset the psychoactive properties of THC.

The magnitude of marijuana’s psychoactive effect depends on the THC level in the particular strain of plant, which parts of the plant are used, and the route through which the drug enters the body. Legalization in some states has led to the breeding of strains that are three to seven times more potent than those available three decades ago.

The impact of smoked or inhaled marijuana is generally felt within a few minutes and lasts two to four hours. Marijuana ingested in food or beverages kicks in more slowly and lasts longer.

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