The Impact of Cannabis on the Cardiovascular System
Understanding the impact of cannabis on the cardiovascular system is crucial to ensuring safe usage, whether for recreational or medicinal purposes. It is well known that cigarette smoking increases the risk of heart disease and heart attack. If cannabis were to cause an increased cardiovascular risk similar to that of cigarettes, any potential benefit from cannabis would likely be outweighed by the harm it could cause to the cardiovascular system. I am going to briefly review the literature for you on this topic and will summarize the most relevant information we have to date.
Immediate Effects of Cannabis on the Cardiovascular System
The macroscopic effects of cannabis on the cardiovascular system have been known since the 1970s. In a paper by Gash et al., cannabis was shown to acutely increase heart rate and decrease the stroke volume of the heart (amount of blood delivered by the heart with each beat), with an overall increase in total cardiac output. The study also showed an increase in the levels of an excitatory compound called norepinephrine in the body while under the influence of cannabis, as well as a minimal increase in blood pressure. All of these findings suggest that cannabis use may increase the stress within the cardiovascular system. With acute increases in cardiac stress, it is important to examine whether cannabis predisposes its users to more serious outcomes.
Cannabis Use and Angina
Angina is a type of chest pain caused by coronary artery disease and represents increased stress on the heart. It is often described as a squeezing, tightness, or pressure-like pain. Angina occurs when the heart muscle does not get enough blood flow for the work that it is doing. Research shows that inhaled cannabis use decreases the time or activity required to cause angina. These findings were only shown to be the case in people who already had known coronary artery disease. With decreased time to angina in certain populations, it is important to examine whether inhaled cannabis use leads to an increased risk of heart attack.
Cannabis Use and Heart Attacks
Available studies on the impacts of cannabis use as related to heart attacks are inconclusive and flawed. The medical study that is cited by all others (Mittleman et al.) found a 4.8x increased risk of heart attack in the 60 minutes following cannabis inhalation (but not when inhaled >60 minutes prior). If this were the case, then it is likely that no benefit from cannabis could possibly outweigh the potential hark for most patients. However, this study had major flaws that essentially make the reported increased risk of heart attack somewhat inconclusive. Out of the 3,882 subjects examined, only 9 had used cannabis in the 60 minutes preceding a heart attack, 3 of which had used cocaine during this time (which is known to increase the risk of heart attack by ~25x). Excluding those 3 subjects, the risk decreased to 3.2x, but this outcome is then based on the data from only 6 people. No medical or surgical practices would ever be changed on the basis of data from 6 people, and I do not believe that this study should influence medical practice. Furthermore, only two studies have examined the impact of cannabis use on mortality after a heart attack. One study found a non-significant increase in mortality, but the subjects who died were mostly male and were tobacco users and heavy alcohol drinkers, all of which contribute greatly to mortality. The other study also showed an increase in mortality, but most of the subjects who died in this study had either AIDS or cancer, both of which greatly increase the risk of death.
Based on the available research, it appears that in the 1-2 hours after users inhaled cannabis, there was a slight increase in stress on the cardiovascular system, but the study does not give enough information to state that there is an increased risk of heart attack as a result of consumption. All of this information leads back to the question anyone should ask when considering medical cannabis therapy: do the benefits outweigh the risks? From a cardiovascular standpoint, it seems that based on the available data, cannabis is safe to use for most patients, as there has been no significant data reporting an increased risk of mortality. For patients with known cardiovascular disease or prior heart attacks, it is likely still safe, although its safety would need to be determined on a patient-by-patient basis and would depend on other risk factors. As cannabis use grows for both recreational and medicinal purposes, it will be important to continue to examine these populations for changes in cardiac risk.