Cannabis & Its Effect on the Heart: It’s Complicated

Kevin Smith, director of cult films such as “Clerks,” “Mallrats” and “Jay and Silent Bob Strike Back,” says cannabis saved his life.

Back in 2018, the writer/director suffered a massive heart attack—a kind that only 20% of patients survive and that doctors call “the widowmaker.” But Smith had been smoking a lot of cannabis earlier in the day, and he says his doctors told him that all of that marijuana may have saved his life.


How? It isn’t completely clear—though Smith credits his consumption for keeping him calm and relaxed during his heart attack, something his doctors said kept his condition from deteriorating further.

Today, Kevin Smith is healthy and back at work. No word on whether he’s still consuming cannabis, but his story highlights the contradictory and often confusing evidence about cannabis’s effects on the heart.

Considerable research shows that cannabis can contribute to increased rates of heart attack and stroke, especially in people who already have some form of heart disease.

But recent research reveals some surprising discoveries about the benefits of cannabis—and tetrahydrocannabinol (THC) in particular—for a healthy heart.

How Does Cannabis Affect the Heart?

The Cannabis sativa plant contains over 100 different compounds and terpenes—oils that add flavors and scents to all plants.

Each cannabis strain has its own unique profile of cannabinoid compounds and terpenes, but they all contain significant amounts of two major cannabinoids: THC and cannabidiol (CBD). Though the proportions of CBD and THC can vary across strains, these two compounds account for many of the various effects cannabis can have on your health.


CBD has a long list of documented health benefits. It doesn’t get you high like THC can, but it has been reported to:

  • Relieve pain
  • Fight inflammation
  • Protect the delicate neural structures of the brain

THC is responsible for the classic marijuana euphoric high, as well as many of the potential undesirable side effects of consuming cannabis, such as:

  • Anxiety
  • Paranoia
  • Agitation

These compounds and others trigger receptors in the body’s endocannabinoid system (ECS), a widespread network that responds to cannabinoid chemicals produced naturally by the body as well as ones from outside sources, mainly the cannabis plant.

Whether it’s smoked, vaped or consumed some other way, natural cannabis with the full complement of compounds and terpenes has a number of complex effects on the heart and blood vessels. These include:

  • Elevated blood pressure
  • Rapid resting heart rate
  • Dilated blood vessels, which cause red eyes and flushing

Some research also indicates that the risk of a heart attack or stroke can rise dramatically in the hour after consuming cannabis, especially if it’s smoked. This risk is greater, too, if a person has an existing heart condition; scientists think THC is to blame for these risks.

But the plant can also improve a person’s survival rate after a heart attack or stroke. Recent research indicates that cannabis could reduce the risk of a condition called atrial fibrillation, a type of irregular heartbeat, in people who are already experiencing heart failure.

Now, some studies suggest that for reasons that remain unclear, THC, as well as CBD, can have some unique benefits for helping the heart.

What Causes Coronary Artery Disease?

Coronary artery disease is the most common form of heart disease, and it’s one of the leading causes of death in the US. Atherosclerosis, or “hardening of the arteries,” causes coronary artery disease. That’s a process in which plaque builds up on the walls of arteries that supply blood to the heart and brain.

Plaque is a combination of:

  • Cholesterol deposits
  • Fatty substances
  • Other kinds of cells

When all of this accumulates on artery walls, they become stiff and narrow. Over time, accumulated plaque can reduce the flow of blood, or even block it entirely, causing a heart attack.

Plaque deposits can also break off and travel to other blood vessels, where they can block blood flow and cause strokes.

THC May Protect Arteries

Treatment for coronary artery disease includes lifestyle changes such as:

  • Quitting smoking
  • Performing regular exercise
  • Taking powerful drugs such as beta-blockers and statins

Surgery may be needed to clear blocked arteries or place a stent to help blood flow.

But some studies suggest that THC can affect ECS receptors in the arteries themselves to reduce the buildup of plaque.

In a study reported in the British Journal of Psychopharmacology, researchers found that people with atherosclerosis have elevated levels of a certain type of cell, called foam cells.

These cells gravitate to the fatty deposits on artery walls, where they ingest low-density lipoproteins—the LDL cholesterol that’s popularly known as bad cholesterol. This gives them an easily identifiable foamy appearance. As they accumulate, they form the plaque that causes the narrowing and blockage of arteries.

The ECS is made up of receptors, called CB1 and CB2. These receptors are found in varying amounts throughout the body’s cells and tissues. According to research, the foam cells that cause artery plaque contain CB2 receptors. When THC activates these receptors, it appears to prevent foam cells from depositing fatty plaque on artery walls.

Low doses of THC may also protect the arteries from damage that LDL cholesterol causes. Oxidation of cells causes the release of free radicals, toxic byproducts that can damage cells and accelerate their decay.

When LDL cholesterol oxidizes, it can produce inflammation that damages artery walls. But low doses of THC also seem to inhibit the activity of an enzyme that oxidizes LDL cholesterol. This reduces inflammation levels that also contribute to coronary artery disease.

The relationship between cannabis and the heart is complex, and scientists are still working to understand why cannabis can protect the cardiovascular system under some circumstances and raise the risk of heart attack and stroke in others. But recent discoveries about THC’s power to affect artery plaque could point the way to new, safer ways to protect the heart.

Photo credit: Microgen/

If you’re new to cannabis and want to learn more, take a look at our Cannabis 101 index of articles. And if you have questions about cannabis, ask them and our community will answer.


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