Two Studies Link Cannabis Use To Substantially Higher Risk Of Heart Attack

Two new studies highlight the potential risks to heart health among young adults who use cannabis. Olena Bondarenko/Getty Images

• A retrospective study found that cannabis users were six times as likely to have a heart attack compared to non-users.
• A meta-analysis of 12 previous studies showed that cannabis users had a 50% higher risk of a heart attack than non-users.
• Both studies lacked sufficient information to determine whether the risk was different for inhaled cannabis versus ingested products.

As legal use of cannabis in the United States has increased in recent years, so have concerns about potential negative health effects.

This includes the impact on the heart. Two new studies found that people who use cannabis are more likely to have a heart attack compared to people who do not use the drug.

These findings are from a retrospective study that will be published in the journal JACC Advances and a meta-analysis of 12 previously published studies being presented on March 29 at the American College of Cardiology’s Annual Scientific Session.

In the retrospective study, researchers found that cannabis users under the age of 50 were more than six times as likely to have a heart attack compared to non-users. The meta-analysis showed that cannabis users had a 50% increased risk of a heart attack.

The meta-analysis included 12 previous studies, with over 93,000 cannabis users and 4.5 million non-users. This is the largest pooled study of its kind to date.

“Asking about cannabis use should be part of clinicians’ workup to understand patients’ overall cardiovascular risk, similar to asking about smoking cigarettes,” study author Ibrahim Kamel, MD, clinical instructor at the Boston University Chobanian & Avedisian School of Medicine, said in a news release.

In addition, “a fair warning should be made so that the people who are consuming cannabis know that there are risks,” he said in the release.

Effects of cannabis use on heart health

The retrospective study used patient data from TriNetX, a global health research network that provides access to electronic medical records. 

Researchers followed patients for an average of over three years. Compared to non-users, cannabis users had a:

• six times higher risk of heart attack
• four times higher risk of ischemic stroke (which occurs when a blood clot or plaque blocks blood flow to the brain)
• two times higher risk of heart failure
• three times higher risk of cardiovascular death, heart attack or stroke.

Participants were younger than 50 and did not have any cardiovascular-related health problems at the start of the study.

Their blood pressure and low-density lipoprotein (LDL) cholesterol levels were within a healthy range. They did not have diabetes or prior coronary artery disease and did not use tobacco products.

For the meta-analysis, researchers included 12 previously published studies, which they rated as being of moderate to good quality. One study was conducted in Canada, one in India, and the rest in the U.S.

The average age of participants in these 12 studies was 41 years. However, some studies did not include information about the participants’ ages.

Of these studies, seven found that cannabis use was linked to a higher risk of heart attack. Four studies showed no difference in heart attack risk between cannabis users and non-users. One study found that cannabis users had a slightly lower risk of heart attack.

When researchers combined the data from all the studies and analyzed this pooled data, they found that active cannabis users were 1.5 times more likely to have a heart attack compared to people who were not current users.

One study included in the meta-analysis found the heart attack risk peaked about one hour after cannabis use.

However, because of differences in the data among the studies, researchers were not able to account for several factors that might affect the results, such as how much and how long participants had used cannabis, and their use of tobacco or other drugs.

“A confounding factor, as indicated in this study, is whether other forms of drug use may contribute to adverse cardiovascular effects,” said Hoang Nguyen, MD, an interventional cardiologist at MemorialCare Heart & Vascular Institute at Orange Coast Medical Center in Fountain Valley, CA, who was not involved in the research.

For example, “cocaine has been known to be detrimental to the heart as it may cause heart attacks and weaken heart muscles, leading to heart failure,” he told Healthline.

Risks of inhaled versus ingested cannabis

Sameer Amin, MD, cardiologist and chief medical officer at L.A. Care Health Plan, who was not part of the research, said more research is needed on the health risks of cannabis.

But “based on [this] early information showing an association of cannabis with an increased risk of worse cardiovascular outcomes, there appears to be an emerging concern,” he told Healthline.

The possible mechanisms for how cannabis might damage the cardiovascular system is not fully understood. 

The researchers suggest that cannabis may affect heart rhythm regulation, increase the heart muscle’s need for oxygen, and contribute to dysfunction of the lining of the arteries. This could make it harder for blood vessels to relax and expand properly, which might interrupt the flow of blood.

In terms of whether inhaled cannabis or ingested cannabis may have a bigger impact on heart attack risk, Kamel said both the meta-analysis and the retrospective study lacked detailed information to determine this.

So “an interesting aspect to look at [in future studies] is whether there are differences between the inhaled form of cannabis versus consumables such as brownies, gummies and candies,” said Nguyen.

Research on other chemicals, though, suggests that inhalation may carry certain health risks.

“We know that chronic inhalation of tobacco and other chemicals damages the lungs and increases several respiratory risks, including things like COPD and lung cancer,” said Andrew Meltzer, MD, MS, professor of emergency medicine and attending physician at the GW School of Medicine & Health Sciences, who was not involved in the new research. 

“But we don’t know for sure if that’s also true with cannabis, because those studies haven’t been done,” he told Healthline.

Is any amount of cannabis ‘safe’?

“It would be challenging to determine the safety of any amount [of cannabis] without conducting clinical trials or bench work,” said Kamel. “However, given the available data, we believe that the risk exists.”

Nguyen suggests that the effects of cannabis on the heart may depend on how often and how much people use it, but more research would be needed to determine that.

Given that it’s not clear what a safe amount of cannabis is, Amin recommends that people “avoid use of any substance that would increase your risk of cardiovascular disease.”

Less chronic use, though, may have a much lower risk.

“Intermittent, relatively low-dose use of cannabis is mostly benign,” said Meltzer, but “we don’t have a lot of data on the health effects of long-term cannabis use.”

In fact, “some of the reactions we see are paradoxical. For instance, in patients who are undergoing chemotherapy, cannabis in short doses actually reduces nausea and stimulates appetite,” he said. “But for some people, chronic daily use of cannabis can actually cause nausea and abdominal discomfort.”

In a recent study, he and his colleagues found that these kinds of symptoms — which occur with cannabinoid hyperemesis syndrome — could represent a costly and largely hidden public health problem.

With the increased legalization of cannabis in the U.S., Meltzer said there’s essentially an active public health experiment going on, one that requires cannabis users to stay up to date about research on the health risks of this drug.

“Unless we carefully monitor this, there’s the possibility that we might find out in 10 years that there are increased medical problems related to long-term use of cannabis,” he said.