The number of Americans at risk of heart attack and stroke has increased substantially over the last decade. According to statistics released from the American Heart Association, nearly half of all adults in the United States have high blood pressure.
Alarmingly, the rising prevalence of hypertension has coincided with the relaxation of U.S. state marijuana laws, raising questions and concerns among both health professionals and the public. People want to know, does marijuana lower blood pressure? Or does marijuana raise blood pressure? And, what are the long-term effects of cannabis on cardiovascular health?
An estimated 2 million Americans with an established cardiovascular disease currently use or have used marijuana. In this article, we’ll review the current evidence on the acute and chronic cardiovascular effects of marijuana.
What is Hypertension?
Hypertension (aka high blood pressure) is when the force of blood flowing through your arteries is consistently too high. When a person has hypertension, their heart must work harder to pump blood around the body, which contributes to hardening of the arteries. Left unmanaged, hypertension can lead to cardiovascular disease, which is the leading cause of death worldwide, claiming nearly 18 million lives per year. Cardiovascular disease includes heart attacks, strokes, and heart failure.
Blood pressure readings contain two measurements: systolic blood pressure (the first number) and diastolic blood pressure (the second number). Systolic blood pressure measures the force on the artery walls when the heart is contracting. Whereas, diastolic blood pressure is when the heart relaxes between beats.
Blood pressure readings below 180/20 mmHg are considered normal and within a healthy range. However, if your systolic blood pressure rises above 130 mmHg or your diastolic blood pressure rises above 80 mmHg, you have Stage 1 Hypertension, according to the American Heart Association. Once your blood pressure reaches 140/20 mmHg, you’ve hit Stage 2 Hypertension—any higher than you’ve entered Hypertension Crisis.
What Causes Hypertension?
Several factors contribute to the development of hypertension, including obesity, stress, chronic alcohol consumption, physical inactivity, and tobacco use. However, the association between hypertension and marijuana consumption is less clear, primarily due to the restrictions on human trials and the complexity of the drug itself. Marijuana contains over 100 active compounds, called cannabinoids, and each strain contains a unique concentration of cannabinoids. Therefore, the effects differ depending on the product.
Cannabinoids exert their effects through the endocannabinoid system, which consists of endocannabinoids and cannabinoid receptors. Cannabinoid receptors, particularly CB2 receptors, are present on the myocardium (heart muscle), coronary endothelium (surface of arteries), and vascular endothelium (surface of veins).
Specific cardiovascular effects, particularly acute effects, are well understood and extensively documented. For instance, we know that tetrahydrocannabinol (THC), the main psychoactive cannabinoid, temporarily stimulates the sympathetic nervous system. However, research studies investigating the long-term effects of marijuana use on cardiovascular health are limited and often plagued by poor study design or animal models that don’t necessarily transfer to humans.
Also, most studies fail to differentiate between consumption methods, such as smoking marijuana, compared to applying a topical ointment. Frustratingly, there’s also a high degree of generalization, with studies often focusing on THC and neglecting the role of cannabidiol (CBD). Lastly, very few studies distinguish between synthetic and plant-derived cannabinoids. With such limited research, it’s difficult to make concrete conclusions on the link between marijuana and hypertension. However, here is what the current research literature says so far.
Acute Effects: Marijuana and Blood pressure
According to Harvard Health, research has consistently shown that marijuana temporarily raises heart rate and dilates blood vessels, causing a modest dose-dependent increase in blood pressure. Together, these actions force the heart to pump harder, which can be dangerous for people with heart disease.
Research published in Cardiology in Review, suggests that the risk of heart attack is up to four times higher during the first 60 minutes of smoking marijuana. While this does not pose a threat to healthy people, it should be a red flag for people with a known heart condition. Other studies have shown a link between marijuana and atrial fibrillation, a common heart rhythm disorder.
To investigate the above claims, medical researchers at the Society of General Internal Medicine recently reviewed the acute effects of THC of several cardiac parameters, including heart rate and blood pressure. Their analysis included six clinical trials on blood pressure, after excluding studies with animal models and less than 20 participants.
In one randomized controlled trial (RCT), low concentrations of THC (3.55%) caused a drop in systolic blood pressure when smoked or injected. Another clinical trial of more inferior quality also found a decrease in systolic blood pressure at similar concentrations.
Three of the four remaining studies found no significant effect, while one study found an increase in blood pressure. These findings suggest there is insufficient evidence to claim marijuana has any specific acute effects on blood pressure. The analysis also included 14 clinical trials, all of which found that marijuana was associated with tachycardia or increased heart rate.
Chronic Effects: Marijuana and Blood Pressure
Smoking marijuana carries many of the same cardiovascular health hazards as smoking tobacco. A new study, published in the American Journal of Health Behaviour, analyzed data from the 2005-2014 National Health and Nutrition Examination Surveys.
In total, 10,709 American adults were included in the retrospective study. Researchers defined marijuana use as “never” (no lifetime use), “past” (lifetime, not in the past 30 days), and “current” (at least once in the past 30 days). After adjusting for covariables – such as alcohol, tobacco, and other drug use – heavy users (defined as daily) were reportedly twice as likely to have high blood pressure than “never” users. However, no significant differences in blood pressure existed between other categories. These results suggest that heavy marijuana use may contribute to the development of hypertension, while occasional use is unlikely to impact blood pressure in the long term.
In another study, published in the American Heart Association Journal in 2020, researchers examined the effects of THC on the blood pressure of almost 3000 veterans, of whom 800 were current cannabis users and 2098 current non-users. Smoking was the predominant form of consumption (90%). After adjusting for covariables, cannabis users had slightly higher systolic blood pressure. Interestingly, however, current users were less likely to be on medication for high cholesterol (statins), blood clotting (anticoagulants), and an irregular heartbeat (beta-blockers). However, this could be a reflection of health-seeking behaviors. They also had a lower body mass index (BMI), which is a well-established protective factor against heart disease.
Is Marijuana Good for High Blood Pressure?
If you currently suffer from hypertension, you may be wondering whether marijuana can help lower your blood pressure. While the body’s endocannabinoid system plays a key role in regulating critical physiological processes, including cardiovascular function, research is yet to determine a definitive answer.
Animal models suggest that anandamide – the body’s own version of THC– may relax blood vessels and thus help lower blood pressure. But anandamide appears to be triphasic, meaning it produces different effects under different conditions. For instance, under some circumstances, anandamide has a stimulatory effect leading to increased blood pressure.
More rigorous human trials are needed to make any claims about the effectiveness of marijuana as a long-term treatment for hypertension.
Heart Disease? Best to Avoid Marijuana
Smoking marijuana carries many of the same cardiovascular health hazards as smoking tobacco, which is a major cause of heart attack, stroke, and heart failure. Until we have a clearer picture of the connection between marijuana and heart diseases, people with a heart condition or at risk of heart attack or stroke due to hypertension should consider avoiding smoking marijuana of any kind. These recommendations are in alignment with Harvard Health.