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Stirring the Pot: Cannabis Use and Your Heart

Dr. Melanie Bone

By Dr. Melanie Bone

May 12, 2022

Welcome back, readers. Decades upon decades of cannabis prohibition has created a plethora of confusion and misinformation around medical cannabis consumption. This lack of reliable information impacts medical professionals, which came to me recently in the form of a question from one of our readers, who also happens to be a medical practitioner. A reader going by C.W. is curious about the effects of cannabis use and your heart. If you have a medical cannabis question you’d like answered, send it to drbone@highthere.com.

Dr. Bone, I am a medical practitioner and have heard that marijuana is dangerous for the heart. I am confused by what I read. What is your opinion? – C.W.

Dear C.W.,

Thanks for asking that question. There are numerous conflicting articles about cannabis and the heart. I will try to give you some insight. 

Understanding How the Heart Works

The heart is a very complex organ with many moving parts. There are two chambers at the top called the atria, and two at the bottom called the ventricles. Blood is returned to the heart from the rest of the body via the Vena Cava, a large vein that collects blood whose oxygen has been used up, and delivers it to the right atrium. 

The blood then flows through a valve into the right ventricle. The blood is then pumped to the lungs to get the oxygen replenished. Once oxygenated, the blood travels back to the left atrium. From there it crosses into the left ventricle which pumps it out into the aorta to supply the entire body with fresh oxygen. 

For this four-chambered pump to work, there must be electrical impulses that make the muscles contract in such a way as to move the blood along the right pathway. Problems in the heart can be mechanical, relating to the muscle itself or the valves. Problems can also be electrical because the impulses to make the heart beat are found in nerve bundles designed to stimulate the muscle contractions at the right time. 

Lastly, oxygenated blood is needed to supply the heart muscle itself with oxygen by way of the coronary arteries. These can be compromised with plaque and interfere with the health of the heart as well. It is often clots that form on top of the plaque that lead to a heart attack.

Studies on Smoking Cannabis and Your Heart

Most studies on cannabis look for correlations of smoking cannabis and cardiac outcomes.  The reports often published, associate smoking cannabis with high blood pressure, rapid and/or irregular heart beat (arrhythmia) and heart attack. 

There is good evidence to suggest that cannabis has different effects on the heart depending on the dose and the method of consumption. At lower doses of THC, the cannabis will cause the heart to beat faster and the blood pressure to increase. At higher doses of THC, the heart beats more slowly and the blood pressure drops. When the heart beats faster, there is a higher likelihood that there will be irregularities to the beats called arrhythmias.

In a 2019 review of reports about cardiac arrhythmias and cannabis use, there was an in depth review of 2000 papers with key words “cannabis” or “marijuana” and “arrhythmia” yielded 27 cases of arrhythmia. Why these people developed abnormal heart beats after using cannabis is not certain. It could be the direct effect of the THC on the heart or it could be related to lowering the amount of oxygen delivered to the heart muscle that indirectly causes the abnormal heart beats. 

It also could relate to an impact on the electrical impulses in the cardiac muscle. For individuals with a predisposition to heart disease such as those with silent coronary artery disease, cannabis can trigger a more serious event such as a heart attack. It tends to occur much more with inhaled products than with ingested ones such as tinctures or edibles. Interestingly, in the study cited above, only 41 percent of the subjects had a positive urine drug screen for cannabis. 

Just as smoking cigarettes is not good for the heart, inhaling the tars and carbon monoxide associated with combusting cannabis is often compared to inhaling cigarette smoke. In fact, most of the time, negative impacts of cannabis on the heart are described after smoking or vaping, both of which involve the lungs. It is not a stretch to believe that smoking or vaping would be stressful for the cardiovascular system and lead to deleterious outcomes. 

It is important to remember that there is no way to know how many cannabis smokers do not have any issues with their heart and never intersect with the medical system or researchers. By looking at those who have had a cardiac event and then looking back to see if they had used cannabis, the data are retrospective and less accurate. 

Heart Considerations for Consuming Cannabis 

The practical question is whether it is reasonable to require some kind of cardiac evaluation prior to starting cannabis as a medication. Just as we do not test people for allergies before trying medications, given the fact that the risk is low, it is not realistic to ask for a cardiac evaluation prior to initiating cannabis. It is imperative that all practitioners speak to their patients about the risks so they are aware of them. If there is a significant family or personal history of heart disease, then the patient needs to be counseled about the possibility of a negative outcome, at least with smoking or vaping. 

In the six years that I have been practicing cannabis medicine, I have not had a single patient suffer a heart attack or other cardiac event due to their cannabis consumption. For the most part, I find that the cannabinoids help to reduce anxiety and stress. Since many heart attacks are related to anxiety and stress, it is logical to believe that cannabis use may actually lower the risk of cardiac events when used judiciously. 

Dr. Melanie Bone

About The Author

Dr. Melanie Bone

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