Is pot bad for your heart? Truth is... we don’t know yet

As the Canadian Senate officially passes Bill C-45 on Marijuana legalization, the University of Ottawa Heart Institute (UOHI) has looked at the effects of marijuana on the heart the conclusion is still unclear.

Widely published experts in the prevention of heart disease, physician and researcher Andrew Pipe, MD, and behavioural scientist Robert Reid, PhD, both from the Ottawa Heart Institute’s Division of Prevention and Rehabilitation, are raising some concerns about cannabis and heart health. As Dr. Pipe put it, “When we consider marijuana and issues relating to the heart we really are steering into terra incognita.” The long-standing illegal status of marijuana has made it a lower priority for health researchers and posed a hurdle to conducting studies.

“When we consider marijuana and issues relating to the heart we really are steering into terra incognita.”

- Dr. Andrew Pipe, MD

Even if there is a lot of unknown about heart health and cannabis, a 2014 review article in the New England Journal of Medicine summarized the effects of marijuana on all aspects of health. The authors found that marijuana use has been associated with vascular conditions that increase the risk of heart attack and stroke, although the mechanisms by which that happens are not clear. The article also noted that the risk is mainly associated with immediate use of marijuana and isn’t necessarily cumulative.

“There is existing evidence that marijuana use may lead to quicker onset of exercise-induced angina during a stress test among people with heart disease. This suggests another reason why it is not a good idea to use marijuana,” said Robert Reid. He also noted that marijuana use could be problematic for people with an irregular heartbeat, or arrhythmia, because it activates the sympathetic nervous system.

What happens to your heart when you use marijuana?

  • Your heart rate and blood pressure increase, forcing your heart to work harder.
  • If you smoke marijuana, the capacity of your blood to transport oxygen throughout your body, including to your heart, is reduced.
  • The result is strain on your heart, and a reduced ability to handle increased demands.

Another concern frequently raised is the link between marijuana and depression. Depression is a known risk factor for heart disease, in part because it interferes with a patient’s ability to adopt healthier behaviours, and many believe that marijuana use can lead to depression. “We really don’t know whether marijuana causes depression, said Dr. Pipe, or whether people who are depressed use marijuana at least in part as an effort to self-medicate. Either way, it underscores yet another area where more research is needed.”

What are patients to do?

With all this uncertainty, it’s hard to know the wisest course for a patient. Dr. Reid advised that patients start asking their care providers about using marijuana just as they would about alcohol and to use caution, until something more definitive is known. “Based on what evidence there is, as well as common sense, trying this newly legal drug should be approached with caution and that, if you must, then don’t smoke it,” said both Dr. Pipe and Robert Reid.

About the University of Ottawa Heart Institute

The University of Ottawa Heart Institute (UOHI) is Canada’s largest and foremost heart health centre dedicated to understanding, treating and preventing heart disease. UOHI delivers high tech care with a personal touch, shapes the way cardiovascular medicine is practiced and revolutionizes cardiac treatment and understanding. It builds knowledge through research and translates discoveries into advanced care. UOHI serves the local, national and international community, and is pioneering a new era in heart health.

Contact:

Leigh B. Morris
Communications Specialist
University of Ottawa Heart Institute
613-316-6409
lmorris@ottawaheart.ca
Twitter logo@HeartInstitute

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