By the Society of Cannabis Clinicians

It is essential for those who utilize and advocate for cannabis in clinical practice to be aware of the benefits and potential harms. While cannabis has been found to be helpful for a variety of conditions, the science hasn’t fully elucidated all aspects of its clinical use. One example is the nuanced scenario of cannabis for patients with heart conditions. It has been demonstrated in preclinical studies that cannabis has cardioprotective properties that may be clinically beneficial.

Recently a sensationalized, click bait style title came out in CNN entitled, “Young adult cannabis consumers nearly twice as likely to suffer from a heart attack, research shows”. It highlights the September 2021 study published in the Canadian Medical Association Journal. The study claimed, among other findings, that adults under 45 years old who consumed cannabis within the past month experienced almost double the risk of having a heart attack than those who didn’t use it.

This article immediately piqued the interest of members of the Society of Cannabis due to its misguided research protocols and convoluted statistical formulas. It is the mission of the SCC to provide continuing education about the medical use of cannabis and best practices in clinical care. With that comes the need to discern when cannabis would (and wouldn’t) be a valid treatment option. It is key to examine the details of how cannabis works in the body and impacts various conditions and maladies.

In an effort to set the record straight on the questionable conclusions presented in this cannabis and heart attack risk study, SCC Board Members Sherry Yafai, MD and Patricia C. Frye, MD weigh in with their observations and research evidence.

The statistics in this study were flawed

Sherry Yafai, MD: This paper did some ridiculous tumble twisting statistics in order to get the findings they wanted. You could feel them pulling to create this result that cannabis use can increase the likelihood of a heart attack. The data weren’t straightforward at all. There were a lot of variables that they had to account for. Some of them they simply didn’t account for, which makes it a poor study.

The researchers used a regression model for statistical analysis and had to adjust for alcohol usage in the study population. Around four times the number of alcohol users were in the cannabis use group leading to a disproportionate number in the cannabis user group. When considering that alcohol abuse alone is tied to atherosclerosis and has been proven to lead to cardiovascular disease, could this factor alone change the results in this survey? It was unclear how this was accounted for in the statistical analysis. The study did not collect any information on the use of cocaine and other illicit substances, leaving a gaping hole in the evaluation.

Patricia C. Frye, MD: Nor did they address the reasons people used cannabis. They didn’t discuss any type of mental health issues, like chronic stress or other conditions that should have been accounted for as well.

Cannabis may contribute to an irregular heart rate in some situations

Frye: Cannabis can certainly increase heart rate in some patients. So anything that might raise the heart rate could increase the risk of an arrhythmia, such as atrial fibrillation. But atrial fibrillation is a condition of aging. Tachycardia is more likely to occur in the cannabis naive or patients who are using high doses of THC. Another issue is with unstable angina. If THC were to increase heart rate or lower blood pressure in these patients, this could increase oxygen demand in the heart muscle, which could theoretically precipitate a myocardial infarction. But I’ve seen some patients with abnormal ejection fraction in heart failure who have been using cannabis for a long time. They are not experiencing lowered blood pressure or increased heart rate.

Yafai: It is important to pinpoint the smaller groups when addressing this question. In Group A, there are the THC naive patients. Group B are those who are THC competent. Within these groups, the type of medicine and dosage of THC will put people in different categories as it relates to their heart. People who are cannabis naive, use inhaled THC, or large doses of an edible can get an increase in heart rate. They can get a slight decrease in blood pressure. But that’s usually very transient. The cannabis competent group tends not to get these rapid increases in heart rate or changes in blood pressure because they are used to it (desensitized). It’s the same for any other medication. The first time you get morphine, you may become hypotensive. Some people get itchy, some get palpitations, or generally feel really uncomfortable. There are many other medications that have very similar reactions with first time use.

This parallel can be drawn oftentimes to “medical” vs “recreational” users. Medical patients who use small or gradually larger doses of THC routinely tend not to experience a negative change in heart rate. Their bodies are adapted to THC. Medical use tends to be non-inhaled in the vast proportion of patients that I see. Recreational users tend to take a large single dose (inhaled or ingested) and can have a sudden change in heart rate. Other irregular heart rhythms have also been reported. Recreational use tends to be inhalation dominant. With inhalation, you can get rapid changes in heart rate. Whereas with edibles or tinctures, there is a lower THC usage and a higher rate of CBD use. Again, you don’t get these big whopping changes in heart rate or rhythms.

Not all heart diseases are created equal

Yafai: There’s a big difference between heart rhythm irregularities versus cardiovascular disease. One has to do with the diameter of blood vessels and the other involves rhythm. When someone’s heart becomes “irregular”, it can increase the amount of oxygen the heart needs. That’s not cardiovascular disease, it is an increased heart rate. Even exercise raises your oxygen demand because your heart rate goes up. The study reported, “When you end up having this mismatch of oxygen supply and demand, it fundamentally leads to a heart attack.” This is incorrect. Oxygen “mismatch” is a concept that is related to pulmonary (lung) perfusion, not to the heart. A heart attack is the result of complete lack of oxygenation to the cardiac muscle, resulting in muscle death. This is measured by an increase in the cardiac muscle enzyme troponin in the blood. Atypical heart rhythms do not cause heart attacks. Irregular heart beats, without underlying pathology (like atherosclerosis) do not lead to heart attacks.

Frye: You definitely can see atherosclerosis in younger people, even as adolescents. A lot of it comes down to diet. If you eat unhealthy foods with lots of saturated fat, you’ll start to have atherosclerotic build-up. Just because they’re under 44 or 45 doesn’t mean that there may not be any atherosclerotic disease. There are studies indicating that ibuprofen use is associated with increased risk of myocardial infarctions. It had to do with COX-2 inhibition. There’s data that shows even though CBDA is a COX-2 inhibitor in animal studies, it’s not associated with increased risk of infarct and may even be cardioprotective as CBD has been found to be in mouse models. THC has actually been shown to be cardioprotective (Steffens et al. 2005, ​​Waldman et al. 2013).

Yafai: We are seeing the cardioprotective factor of cannabis routinely in many studies and consistently in clinical practice. The heart failure patients I see most often are utilizing cannabis for pain management instead of opiates. There was a specific clinical case study where a patient had continuous coronary artery disease for years that couldn’t be stunted. He had consistent dypsnea or shortness of breath, and chest pain. He was on a ton of opiates. He was eventually able to come off of opiates and had less chest and ischemic pain with the use of cannabis.

Safety Parameters for Using Cannabis Medicine are Essential

Frye: Cannabis is personalized medicine and we need to be able to address this on a case by case basis. I had an 83-year-old patient with unstable angina and atherosclerotic disease who was on nitroglycerin. She couldn’t go up the steps without having shortness of breath. She saw another doctor who gave her no instruction on how to use cannabis. She went to the dispensary and they gave her a 90% THC vape pen when she had never used cannabis before. She was also given a THC only transdermal patch. She came to me on how to use the products and I told her she couldn’t use any of them. People need to be careful with those populations.

Yafai: I always say that people who are on more than two medications, are over the age of 65, or with a history of cardiovascular disease, heart arrhythmias, or dysrhythmias should be talking to a physician before they start cannabis-based medicine. It is the same for any other medication. There can be drug interactions and potential problems. It’s not because of the concern about a heart attack or death. It’s because it may set off a heart abnormality and provoke heart dysrhythmia. Cannabis may lead to low blood pressure, especially in combination with other medications. That can lead to passing out, falling, etc. I feel like seeing a cannabis friendly provider is a far reaching request. But it really shouldn’t be. We should be making dispensaries require it for certain individuals.

People think CBD is easy to take and is suitable for everyone. I actually have the same requirements with CBD. If you take two or more medications, or medications that affect the brain such as antidepressants, opiates, or heart medications, you need to talk to a doctor. Medication/medication interactions happen more often with CBD products than THC products. CBD is more readily available and people often don’t know what they’re getting.

Cannabis and Pharmaceutical Drug Interactions

Frye: I don’t know of any contraindications for CBD and heart medications in general. With CBD and beta blockers, I recommend that they are spaced apart and not taken at the same time. A lot of patients with cardiac conditions may be on warfarin. There are other anticoagulants where there is no interaction. But Warfarin can create some issues. I heard somebody say that it’s contraindicated. I don’t consider anything contraindicated if it’s spaced. In regards to cardiac medication, a lot of these patients are on statins. Certain statins are affected by CBD, but not all of them. Those medications should be spaced so that you don’t raise statin levels; otherwise you could get into rhabdomyolysis or other problems.

Yafai: It has to be monitored, just like with other medications. You don’t give a thyroid medication as a supplementation and then leave it unchecked. You make sure the dosing is right. Doctors get flustered with cannabis because they believe they don’t know the right dosing. But the whole art of medicine is dosing! It lends itself to this art of medicine. If a patient has a history of atrial fibrillation and they want to start THC-based medicines, that’s where I usually start even lower and go very slowly. As long as they adapt to the THC, I don’t see it being problematic for that situation.

With blood pressure medications, such as nitroglycerin, people shouldn’t take them and then have a puff of a THC product right afterwards. That could make someone pass out, resulting in head trauma or a broken hip. But for the majority of people, I have them monitor their blood pressure once they start on cannabis-based medications. That’s not because I’m worried about them fainting, but rather that their blood pressure tends to regulate better. Frequently, we can start dosing down their blood pressure medicine.

The SCC is committed to expanding research and scientific understanding on the use of cannabis in clinical practice. You may learn more about the mission of the non-profit as well as peruse our Clinical Training Curriculum.