IN our previous article we had discussed some of the effects of marijuana on the body, particularly with respect to the heart and blood vessels.

This week we will look at a few studies that have investigated marijuana use and its possible effect on heart and vascular disease. It is important to note that much of the evidence comes from what is known as observational studies. These are studies in which a group of people followed over time. During this period, the use of marijuana is noted and at the end of the study it is determined if marijuana use has been associated with clinical harm or beneficial effects. These studies do not provide the same level of certainty as randomised clinical trials; however, can be important in raising initial concerns. Many things that we now know to be harmful were first identified in this way eg, cigarette smoking, airborne pollution, lead poisoning, etc. The major challenge with conducting randomised studies of marijuana use is that in most countries its use is illegal or highly restricted. This makes acquiring the plant for research as well as obtaining funding difficult.

Short-term cardiac effects of marijuana use

As we had discussed previously the use of marijuana which is high in delta-9-tetrahydrocannabinol (THC) is associated with stimulant effects on the heart and blood vessels. These effects include faster heart rates, elevated blood pressure, increases in the amount of work done by the heart, increases in inflammation and the likeliness of the blood to form clots. Small studies have suggested that marijuana use is associated with an increased risk of heart attack, abnormal heart rhythms and stroke immediately after smoking. It should be noted that these studies were small and significantly limited by several factors. These include not considering other risk factors for heart disease, biases in the way patients were selected and by not quantifying the amount or route of marijuana use. An interesting observation is the trend in death rates from cardiac disease in American states that have legalised marijuana use. These rose on average 2.3 per cent in men and 1.8 per cent in women as opposed to states where marijuana use remains restricted.

Long-term cardiac effects of marijuana use

There are very few well-designed studies that look at the long-term outcome in chronic marijuana users. One study which did not support significant harm is the CARDIA study. This study, which reported results in 2017, followed young adults. At the start of the study risk factors for heart disease were quantified and they were followed for 25 years starting in 1984. At the start of the study approximately 5,000 participants, who were 18-30 years of age, were enrolled. Eighty-four per cent of the enrolled population used marijuana. In this study the use of marijuana did not appear to increase the risk of heart disease, stroke, coronary artery disease or cardiac death.

A larger study from the United Kingdom was reported in 2022. This took data from the UK Biobank study, which is a large observational study of 500,000 men and women in England, Wales and Scotland who were recruited between 2006 and 2010. The ages at recruitment were 40-69 years of age. Marijuana use was reported in approximately 35,000 people of which 11,000 used marijuana monthly. They found that in their cohort marijuana use was associated with a decreased risk of heart attacks with higher levels of use seeming to be protective. In contrast to the above two studies, preliminary data suggesting adverse effects for marijuana on the heart was presented at the American Heart Association and American College of Cardiology meetings this year.

“All of Us” is a National Institutes of Health sponsored cohort study with approximately 150,000 participants who were free of heart disease at the start of the study. At the American Heart Association meeting in November preliminary data was presented suggesting that daily marijuana use increased the risk of heart failure by 34 per cent when compared to those who had never use marijuana. Earlier this year at the American College of Cardiology meeting data from the “All of Us” cohort was presented looking at the risk of coronary artery disease. The authors found that daily use of marijuana increased the risk of coronary artery by about a third in patients who use marijuana daily when compared to non-users. Interestingly, in their study monthly marijuana use did not appear to increase risk. They did not report a protective effect like the UK Biobank study.

Aside from the above, which were well done observational studies, a host of other smaller studies have suggested the possibility of heart and vascular disease from marijuana consumption. Aside from the increased death rates from heart disease in American states that have legalised the marijuana use studies have also found an increased risk of heart attacks and emergency room visits when compared to states that did not legalise marijuana use. Reports have associated weekly marijuana use with an increased risk of stroke or threatened stroke.

What does it all mean?

At this point in time all that we can conclude is that there are some signals suggesting the possibility that marijuana may play a role in the development of heart disease. Based on the pharmacology of the marijuana plant, the two major studied cannabinoids (THC) and cannabidiol (CBD) have deleterious and protective effects on the heart and vascular system, respectively. There is really no standardisation in marijuana products and an individual may be consuming different amounts and ratios of THC and CBD every time they use marijuana. There is little data in the above studies on how marijuana was used ie, ingested, smoked, or vaped and whether one route is safer than the other. There are some reasons to be concerned that smoking marijuana may expose users to much of the harm that comes from traditional cigarettes. Another important point is the change in the potency of marijuana that is available now with much higher levels of potentially harmful THC. Clearly large, randomised studies are needed to answer questions about the cardiac safety of marijuana use.

What should I do?

Marijuana use is important for many segments of our population from religious, cultural, recreational, and more recently medical points of view. From the limited data available CBD use does not seem to have adverse cardiac events and, based on the way it interacts with receptors in the body, may have some protective effects. Based on its physiological effects, THC, or marijuana plants high in THC certainly may be of concern but we currently do not have hard, conclusive evidence at this point in time. Like many things in life, one must weigh the potential risks and benefits of whatever one does. I would encourage those who have heart disease, particularly coronary artery disease, abnormal heart rhythms, hypertension, heart failure, hypertension, and stroke to be cautious with marijuana use. Of particular concern would be smoking marijuana with high levels of THC. It is likely, particularly given increasing legalisation of marijuana use worldwide, that large, randomised studies will be done and reported. This data will hopefully allow us to better answer these questions.

Dr Ernest Madu, MD, FACC and Dr Paul Edwards, MD, FACC are consultant cardiologists for Heart Institute of the Caribbean (HIC) and HIC Heart Hospital. HIC is the regional centre of excellence for cardiovascular care in the English-speaking Caribbean and has pioneered a transformation in the way cardiovascular care is delivered in the region. HIC Heart Hospital is registered by the Ministry of Health and Wellness and is the only heart hospital in Jamaica. Send correspondence to info@caribbeanheart.com or call 876-906-2107.