Cannabis side effects no one wants to talk about, Part 2: What pot does to your heart

We look at the science—inasmuch as that science is available


Photos by Cabezonication (left) and Moussa81 (right). Both photos istock/Getty Images Plus.


Welcome to the second part of our look at some of the less pleasant effects of smoking cannabis. It should go without saying that our intent is not to persuade the public, Reefer Madness style, of the dangers of the demon weed. We simply believe that cannabis users should make informed choices with regards to their health. Last time we talked about the lungs, and this time we’ll be getting to the literal heart of the matter.

To do that, we will be looking at the science—inasmuch as that science is available. As the Heart and Stroke Foundation of Canada points out, “There is currently little high-quality scientific evidence about the impact of recreational cannabis use on heart conditions and stroke.”

But more about that later…


Let’s start with what weed smokers already know firsthand. Health Canada tells us that “cannabis is known to cause peripheral vasodilatation, postural hypotension, and characteristic conjunctival reddening after smoking,” and that “the most consistent acute physiological effect of smoking cannabis is dose-related tachycardia.”

There are a lot of big words there. Let’s just focus on that last bit: smoking weed can make your heart beat faster—that’s tachycardia, defined by the Mayo Clinic as a heart rate over 100 beats per minute.

As Dr. Andrew Pipe, a heart specialist at the Ottawa Heart Institute, told CannCentral in 2019: “Any time you smoke you are inhaling large amounts of carbon monoxide.”

In the article titled “It’s not a heart attack: chest pain from smoking weed”, Kieran Delamont explained: “That makes your heart pump harder to make up for the lack of oxygen in your blood, which serves to stress it even further causing chest pain from smoking weed.

“The lack of oxygen,” Delamont continued, “is the culprit for an effect that many people experience when they smoke weed: a racing heart, especially if you’re smoking dry weed, or weed that produces thick smoke, your heart is being pushed into overdrive, which can also heighten feelings of paranoia.”

Photo by Nenad Cavoski/iStock/Getty Images Plus.

Tachycardia might be bothersome, but it’s not especially concerning, unless you have a pre-existing heart condition. As Health Canada states: “While cannabis-induced tachycardia is not usually considered dangerous for healthy young users, it may be dangerous to those already suffering from cardiac disorders or angina.”

Where it gets confusing

Here’s where things get really confusing, though. Some research has suggested that cannabis can actually have a positive effect on cardiovascular health.

A 2018 study, for example, looked at over one million Americans who had experienced a heart attack (or acute myocardial infarction, in the medical lingo). Researchers found that those who reported using cannabis were at no increased risk of ventricular fibrillation or ventricular tachycardia. What’s more, the cannabis users had a decreased risk of in-hospital mortality and atrial fibrillation (also called AFib). The American Heart Association defines AFib as “a quivering or irregular heartbeat (arrhythmia) that can lead to blood clots, stroke, heart failure and other heart-related complications”.

(Worth knowing is that the authors noted the cannabis users in their study tended to be younger and less likely to have coronary artery disease or coronary risk factors than non-users.)

Research has been limited

That’s the (possible) good news. The bad news is that other research has suggested links between cannabis use and increased risk of stroke and high blood pressure.

The truth is, however, that no one knows for certain exactly how cannabis affects the heart. This isn’t willful ignorance; organizations including the American College of Cardiology and the American Heart Association have cited the need for further research.

In the U.S., at least, the legal status of cannabis is a major roadblock. In a scientific statement released last August, the AHA said as much: “Our understanding of the safety and efficacy of cannabis has been limited by decades of worldwide illegality and continues to be limited in the United States by the ongoing classification of cannabis as a Schedule 1 controlled substance.”

“We urgently need carefully designed, prospective short- and long-term studies regarding cannabis use and cardiovascular safety as it becomes increasingly available and more widely used,” Robert L. Page II, chair of the writing group for the statement, said in a news release. “The public needs fact-based, valid scientific information about cannabis’s effect on the heart and blood vessels. Research funding at federal and state levels must be increased to match the expansion of cannabis use—to clarify the potential therapeutic properties and to help us better understand the cardiovascular and public health implications of frequent cannabis use.”

Illustration by magicmine/iStock/Getty Images Plus.

Hope on the horizon

Its classification as a Schedule 1 substance makes it illegal for U.S. researchers to study cannabis rigorously in controlled clinical trials. Hope could be on the horizon, however. On December 4, the United States House of Representatives voted in favour of decriminalizing cannabis at the federal level.

As CannCentral reported at the time, the lower house of the U.S. Congress voted on the MORE Act of 2019. Also known as House Resolution 3884, the bill “removes marijuana from the list of scheduled substances under the Controlled Substances Act and eliminates criminal penalties for an individual who manufactures, distributes, or possesses marijuana”.

If the U.S. Senate passes the bill and it becomes law, that will open the door to much-needed research.

Mitigating negative outcomes

Where, though, does that leave you, as a medical or recreational cannabis user? How can you mitigate potential negative health outcomes from using weed?

Start by considering cutting down on smoking or vaping, which are generally considered to be the most harmful ways of getting your THC.

As the AHA’s Page said, “If people choose to use cannabis for its medicinal or recreational effects, the oral and topical forms, for which doses can be measured, may reduce some of the potential harms. It is also vitally important that people only use legal cannabis products because there are no controls on the quality or the contents of cannabis products sold on the street.”

As we said in our previous installment, the best way to proceed is to educate yourself as much as possible and, as always, to use your best judgment.

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