Doctors should warn cardiology patients about the risk of marijuana use, say researchers

By Sally Robertson, B.Sc.Jan 20 2020

A team led by investigators at Brigham and Women's Hospital has stated that cardiology patients should be warned and counseled about the potential risks of using marijuana until further evidence is available.

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Despite more states starting to legalize marijuana, and more products becoming available, the effects on heart health are understudied and not properly understood, says the team.

According to a review published today in the Journal of the American College of Cardiology, cardiologists should inform patients about the risks, including the effects marijuana may have on some commonly prescribed cardiovascular medications.

The review, which estimated that more than 2 million people with a cardiovascular disease currently use or have used marijuana, pointed towards a worrying link between smoking the drug and increased cardiovascular risk.

Muthiah Vaduganathan and colleague Ersilia M. DeFilippis assessed responses to the 2016 National Health and Nutrition Examination Survey (NHANES) to estimate how many adult marijuana users in the United States had cardiovascular disease. Of 89.6 million people who reported current or previous use of the drug, an estimated 2 million (2.3%) had a cardiovascular disease in 2015-2016.

“Many more may be at risk"

Since then, more states have legalized marijuana for both recreational use and medical purposes, meaning its use may now be even more widespread.

In addition to the 2 million marijuana users with diagnosed cardiovascular disease, many more may be at risk. With many adolescents and young adults turning to marijuana, it is important to understand the cardiovascular implications they may face years down the line." DeFilippis

The researchers say some observational studies have suggested a connection between marijuana use and a range of cardiovascular problems, including coronary heart disease, smoking-related cardiotoxicity, arrhythmia and cardiovascular events such as stroke.

“For the first time, marijuana users are exceeding cigarette smokers in the U.S.”

Now, their review suggests that smoking marijuana is associated with many of the same cardiovascular health risks as smoking tobacco, says Vaduganathan.

"This was eye-opening for us," he said. "We're experiencing an epidemiological shift. More patients are curbing their cigarette smoking, and we're seeing big improvements in cardiovascular health for those who quit. In contrast, we're seeing an accelerating use of marijuana and now, for the first time, marijuana users are exceeding cigarette smokers in the U.S.”

Vaduganathan adds that, while the level of evidence is modest, there is now enough data to advise highest-risk patients about using marijuana, including those who present with a heart attack or new arrhythmia, or who have been hospitalized with heart failure.

Marijuana can interfere with heart medications

The investigators also encourage physicians to ask cardiology patients about how often and how much marijuana they use because it can interfere with other medications they might be taking.

According to the review, statin levels can increase when used in combination with marijuana as both drugs use the same metabolic pathway - the cytochrome P450 system. The same applies to blood thinners such as warfarin if they are used together with marijuana.

In their review, the authors outline the drug interactions that marijuana can have with commonly prescribed cardiovascular medications.

"The review provides detailed tables of many drugs administered for various cardiovascular conditions, with the anticipated effects of marijuana on each one," says Vaduganathan. "These will be helpful to cardiologists and pharmacists reviewing patients' medications and will help them collaboratively decide whether they need to adjust dosing if the patient continues to use marijuana."

The reviewers advise limiting use as much as possible

The reviewers recommend that patients who wish to continue using marijuana (or have medically indicated reasons for doing so,) limit its use as much as possible.

They also advise that clinicians inform patients that vaping and certain synthetic forms of cannabinoids are particularly potent and may be associated with even greater adverse effects.

"Vaping marijuana is becoming more and more common, and we know vaping marijuana increases the pharmacological effects of the drug," says Vaduganathan.

Studies into cardiovascular health risks have been limited by federal laws

Data on the exact cardiovascular health effects of marijuana are limited, mainly because federal laws that classify marijuana as a Schedule I drug have restricted its use in high-quality research.

However, real-world data can be used to study its effects, by comparing before-and-after health data in states where marijuana has been legalized, for example.

Furthermore, as marijuana use becomes more common in the US, epidemiologists may be able to conduct large-scale studies to verify the link between marijuana and cardiovascular risk.

"Now that we have seen marijuana use becomes more popular than tobacco smoking, we need more rigorous research, including randomized clinical trials, to explore the effects of marijuana on cardiovascular health," advises Vaduganathan.

“It is important for cardiologists to talk to their patients about marijuana use”

DeFilippis says that although more data are still needed, the evidence so far indicates that marijuana use has been associated with coronary artery disease, arrhythmia, cardiomyopathy and more.

"Therefore, asking patients about marijuana use may help in risk assessment. Also, we know that marijuana use affects the metabolism of many common cardiac drugs. To make sure patients are getting therapeutic doses without untoward side effects, it is important for cardiologists to talk to their patients about marijuana use,” she concludes.