Cannabis and Your Heart: Unresolved Issues

This past week, the American Heart Association released its long awaited scientific statement on the effects of cannabis on cardiovascular health. This document provides an excellent summary of available evidence to date, but it is important to note that data are limited. This limitation is largely due to the fact that cannabis is still classified in the U.S. as a Schedule 1 controlled substance, meaning that it has no currently accepted medical use and has a high potential for abuse. Consequently, research funding for well-designed studies aimed at understanding the effects of cannabis on the cardiovascular system have been non-existent. Instead, we’ve relied upon weaker evidence derived from observational studies to help define the problem. It is exceedingly hard to believe that in 2020, cannabis remains in the same category as two other Schedule 1 controlled substances, heroin and LSD (neither of which of course are legal for purchase, either medically or recreationally). Consequently and as aptly pointed out in the AHA document, the first (and second) order of business is: 1) removal of cannabis from Schedule 1 of the U.S. Controlled Substances and 2) removal of all legal barriers in order to permit research funding and well-designed clinical trials. Current evidence suggests that cannabis has opposing heart-related effects depending upon its formulation. That is, cannabis products containing pure THC can have adverse effects on the heart while those containing pure CBD may have beneficial effects.

1. THC Potency and Administration: The potency of THC containing cannabis changed significantly in 1996 when California became the first state to approve marijuana for medicinal purposes. A marijuana induced “high” occurs following inhalation of a joint with an average THC content of 7.5 mg (onset: seconds-minutes/duration: up to 3 hours) or after consumption of an edible at a THC dose of 10 mg (onset: 30 minutes-2 hours/duration: up to 8 hours). High doses (e.g., 30 mg THC or greater) are more likely to produce adverse effects as was the case in a 70-year old man who suffered a heart attack after sucking a marijuana lollipop in a single sitting; the THC content of that lollipop was 90 mg! Users of marijuana prior to 1996 who are now considering its medicinal or recreational use would be surprised to learn that the content of THC is now ~3-fold higher. Consequently, a higher likelihood of adverse effects is more likely to be encountered especially when other risk factors co-exist (e.g., cigarette smoking/vaping) or when certain medications are prescribed (refer to AHA document for details). Side effects include acute rise in blood pressure, rapid heart rate and/or abnormal heart rhythm, most notably atrial fibrillation. In American states where cannabis is legal, hospitalization for heart attacks have increased and the risk of stroke has been reported to be 3-fold higher in frequent users (at least once a week) compared to less frequent or non-users. As with other therapies, benefit versus risk should always be assessed with the lowest amounts recommended to achieve the desired effect.
2. CBD Potency and Administration: In contrast to marijuana/THC cannabis, CBD cannabis is derived from the hemp plant that was excluded from the Control Substances Act and legalized in the 2018 Farm Bill. Like THC products, CBD can be inhaled (onset: 3-5 minutes/ duration: up to 3 hours), consumed (onset: hours/ duration 12-24 hours) or applied as an oil. CBD containing products may not only help to reduce anxiety and emotional stress but also exhibit anti-inflammatory properties which may help to reduce the risk of heart disease. In one small study of healthy volunteers, a single dose of 600 mg CBD lowered systolic blood pressure by 5 mmHg in response to stress (about 1/2 the amount observed with a blood pressure medication). In another small scaled study of volunteers with heightened anxiety, oral administration of 400 mg CBD was associated with reduced levels of anxiety. Despite encouraging preliminary data, large clinical trials are required to determine whether regular use of CBD reduces the risk of heart disease. In addition, the optimal CBD dose for specific conditions have yet to be determined. Finally, regulation of CBD products will also help to protect consumers against product impurities. The new AHA statement will hopefully set the stage for addressing these unresolved issues and advancing this growing field.

Michael Miller, MD is Professor of Medicine, Epidemiology & Public Health at the University of Maryland School of Medicine in Baltimore, Maryland USA.  His latest book is  “Heal Your Heart“ published by Penguin Random House.