In late February 2024, a study published in the Journal of the American Heart Association (JAHA) caught the attention of the popular press, resulting is some rather dire headlines. Typical of this was a story on CNN’s website that proclaimed: Any use of marijuana linked to a higher risk of heart attack and stroke, study says, followed up by a subhead that warned: The danger is real for young and old alike.
At first glance, these assertions might influence some patients to moderate their medical marijuana therapy or discontinue therapies altogether. But, as is often the case when research is interpreted for popular audiences, the headlines don’t always tell the full story or reflect the nuances of the scientific method. That said, the study does raise some valid concerns that should be addressed and assessed by any responsible medical marijuana patient.
The JAHA Marijuana Study
The study behind the headlines is titled “Association of Cannabis Use With Cardiovascular Outcomes Among US Adults.” Funded by the National Cancer Institute and National Heart, Lung, and Blood Institute, the stated goal of this research project was to “assess the association of cannabis use (number of days of cannabis use in the past 30 days) with self‐reported cardiovascular outcomes (coronary heart disease, myocardial infarction, stroke, and a composite measure of all three).”
Findings from this study were based on self-reported data from the Centers for Disease Control and Prevention (CDC) “Behavioral Risk Factor Surveillance Survey” which the agency describes as “a system of health-related telephone surveys that collect state data about U.S. residents regarding their health-related risk behaviors, chronic health conditions, and use of preventive services.”
Beginning in 2016, the CDC added a new question to the phone survey, asking participants: “During the past 30 days, on how many days did you use marijuana or hashish?” Answers were subsequently compared to survey data from respondents who reported indications of prior or current coronary heart disease (CHD), myocardial infarction (MI), and stroke. These risk assessments were made based on answers to the question, “Has a doctor, nurse, or other health professional ever told you that you had angina or coronary heart disease, heart attack, or stroke?” After compiling the responses the study authors created a model they considered to be a composite indicator for cardiovascular disease.
This was the largest survey of its type to date, involving more than 430,000 respondents between the ages of 18 and 74. Survey modeling took into account factors such as age, demographic and socioeconomic factors, health behaviors, and chronic conditions. The study also separated respondents who had never smoked tobacco, never smoked marijuana or smoked both tobacco and marijuana.
Based on respondents’ answers to their cannabis use days in the previous month, the authors created a linear model that compared frequency of cannabis use to the self-reported information on coronary disease incidents. This modeling was the basis for the study’s concluding statement, which has since garnered the headlines:
Cannabis use is associated with adverse cardiovascular outcomes, with heavier use (more days per month) associated with higher odds of adverse outcomes.
Because cannabis use information was limited to a simple yes/no response on frequency of use, the study did not contain the specific information needed to take a deeper dive into the specific composition, delivery method, or quantity of cannibals consumed by respondents. Other survey constraints noted by the authors included the unavailability of data on participants’ baseline lipid profile or blood pressure, and the possibility that, due to the greater number of younger respondents, there was a potential underestimation of atherosclerotic disease, which is a process that evolves over decades.
Study Problems
Several weeks after the JAHA study was published, the Medscape Journal of Medicine published a commentary authored by Perry Wilson M.D., who is an associate professor of medicine and public health and director of Yale’s Clinical and Translational Research Accelerator. Wilson begins by acknowledging the thorough process by which study data was compiled, managed, and adjusted to obtain the most accurate interpretation possible. However, he then points out what he calls a “couple of problems with the methodology.
Wilson writes:
First, like most survey studies, this one requires honest and accurate reporting from its subjects. There was no verification of heart disease using electronic health records or of marijuana usage based on bio-samples.
While conceding that:
Broadly, miscategorization of exposure and outcomes in surveys tends to bias the results toward the null hypothesis, toward concluding that there is no link between exposure and outcome, so perhaps this is okay.
Wilson then goes on to raise what he calls the primary concern of the methodology.
The bigger problem is the fact that this [study] is a cross-sectional design. If you really wanted to know whether marijuana led to heart disease, you’d do a longitudinal study following users and non-users for some number of decades and see who developed heart disease and who didn’t. Here, though, we literally can’t tell whether people who use marijuana have more heart attacks or whether people who have heart attacks use more marijuana.
The Journal of Palliative Medicine notes that cross-sectional studies are well suited to identifying the prevalence of a given condition, but due to their “snapshot” time frames, are less suited to identifying direct cause-and-effect relationships. The explanation given is that:
The primary limitation of the cross-sectional study design is that because the exposure and outcome are simultaneously assessed, there is generally no evidence of a temporal relationship between exposure and outcome. That is, although the investigator may determine that there is an association between an exposure and an outcome, there is generally no evidence that the exposure caused the outcome.
Another point Wilson raises is the way the authors applied a dose-response relationship between marijuana use and these cardiovascular outcomes. He writes:
The model used classifies marijuana use as a single continuous variable ranging from 0 (no days of use in the past 30 days) to 1 (30 days of use in the past 30 days). The model is thus constrained to monotonically increase or decrease with respect to the outcome. To prove a dose response, you have to give the model the option to find something that isn’t a dose response — for example, by classifying marijuana use into discrete, independent categories rather than a single continuous number.
Wilson ends by noting that his critique of the study was not intended to invalidate or downplay its conclusions, and instead point out the need for additional research that can provide more specific and accurate risk assessment models.
Risk Assessment
Several recent studies on the relationship between cannabis use and heart health provide mixed information on the potential risks of adverse coronary events related to cannabis use.
A 2020 position statement from the American Heart Association stated that, based on currently available information:
Cumulative lifetime and recent cannabis use did not show an association with incidence of cardiovascular disease, coronary heart disease, or cardiac mortality.
With the caveat:
Evidence is still inconclusive for cannabis use and adverse cardiovascular outcomes, resulting in an urgent need for carefully designed, prospective short- and long-term studies.
In October 2022, the European Heart Journal published the results of a Danish study that found that patients who were prescribed medical cannabis for chronic pain conditions showed an increased risk of heart arrhythmias, but also concluded that the use of medical cannabis was not associated with an elevated risk of acute coronary syndrome or heart failure.
In contrast, a news release for the Heart Rhythm Society’s Annual Scientific Session proclaimed: “New Study Suggests Marijuana Use Does Not Increase Risk of Heart Arrhythmias, Instead May Reduce Risk of Afib.”
The release summarized the results of a broad-based study comparing clinical profiles and in-hospital outcomes between marijuana users versus non-users from 1994 to 2013. The authors reported:
According to new research, smoking marijuana may not be associated with an increased risk of ventricular fibrillation (VF) and ventricular tachycardia (VT) following an acute myocardial infarction (AMI), or heart attack. [The study also indicates] that marijuana users had a decreased risk of atrial fibrillation (AFib) and in-hospital mortality.
A study reported in the December 2023 issue of BMC Cardiovascular Disorders noted:
Causality between cannabis use and atherosclerotic cardiovascular disease (ASCVD) is challenging to assess in observational studies due to recall bias, inadequate exposure assessment, non-exhaustive inclusion of confounders or weak methodology design.
The authors sought to overcome some of these limitations by employing a model known as Mendelian randomization, which uses genetic markers to identify a causal association between a potentially harmful exposure (cannabis) and a disease outcome (ASCVD). Based on modeling that compared never-users to ever-users, the authors stated they:
…could find no causal effect of cannabis use on the risk of coronary artery disease (CAD) or acute ischemic stroke (IS).
While adding that:
Further studies are needed to replicate our findings, and to investigate more precisely the risk of ASCVD in relation to the quantity, type, route of administration, or the age at exposure to cannabis.
In light of the currently available information on cannabis use and heart health, there are several potential risk-mitigation strategies that responsible medical marijuana patients should keep in mind when choosing a therapy. First is the importance of working with qualified medical cannabis physicians; second is choosing a product of known content that delivers an appropriate dose of medication in the safest possible format; and third is the importance of obtaining pure and properly identified products from a trusted source.
Clearing the Smoke
Popular reporting by NBC News referenced two recent studies that sought to identify a link between marijuana use and cardiovascular issues. The reporting included a quote from a clinical pharmacist at the University of Colorado who was “very worried” by the news. The report then went on to quote Dr. Peter Grinspoon, who was identified as “one of the leading cannabis researchers in the U.S.”
[Grinspoon] said that while it’s important to note the two studies do not directly prove marijuana causes heart problems, it’s an issue that needs to be urgently looked at.
And added:
Although most studies have looked at people who smoke marijuana, more data is needed, Grinspoon said. His best guess is that it’s the smoke as opposed to the marijuana itself that may be affecting our hearts.
While the question of smoked marijuana’s effect on heart health may require additional research, there are indications that smoked marijuana may not pose the same risks to lung health as tobacco. CannaMD has previously reported on the subject and cited a study published in the Journal of the American Medical Association which reported:
Light to moderate marijuana consumption did not appear to have an adverse effect on pulmonary function.
CannaMD‘s reporting also includes the advice that:
Patients who have concerns over their susceptibility to smoked cannabis might consider alternate delivery methods that are known to provide equivalent dosages with a similar response time.
The most common alternative is a water filtration pipe, which provides a similar time of delivery. Edible formulations can also be quite effective but typically have a delayed response time for delivery. Another risk-mitigation strategy that patients who prefer smoked delivery can employ is the adoption and responsible use of higher-potency formulations that deliver the suggested dose of medication with a shortened inhalation period.
For any of these strategies, it is advised that patients consult with a cannabis-qualified physician such as those in the CannaMD network.
Sourcing Pure Products
A 2021 study on cannabis and cardiovascular health summarizes the concerns associated with cannabis obtained from questionable or black-market sources. The authors write that:
The large market of cannabis has given rise to numerous potentially hazardous natural contaminants or artificial adulterants being reported in crude cannabis and preparations.
Among the mentioned hazards:
- Microbial contamination (e.g., fungi and bacteria), pesticides, and heavy metal contaminants introduced during cultivation and storage
- Growth enhancers and pest control chemicals
- Intentional contamination for profit purposes by adding substances (e.g., tiny glass beads and lead) to increase the weight of the cannabis product
- Psychotropic substances (e.g., tobacco and calamus) and cholinergic compounds are added to either enhance the efficacy of low-quality cannabis or to alleviate its side effects
These concerns emphasize the importance of consuming pure and properly identified medical cannabis products obtained through a legal and reliable source.
CBD Benefits & THC Risk Mitigation
An additional factor that may play a role in heart health as it relates to cannabis therapies is the specific content of the product. More specifically, the product’s CBD and THC content.
Most research suggests that CBD is not a risk factor for cardiovascular disease, and may provide some benefits. A study published in the British Journal of Clinical Pharmacology examined the potential cardioprotective effects of CBD and reported that under laboratory conditions:
CBD treatment does not appear to have any effect on resting blood pressure or heart rate, but does reduce the cardiovascular response to various types of stress.
The study listed potential therapeutic roles for CBD in cardiovascular disorders, including anti-inflammatory responses, stroke recovery, and the vasorelaxation of preconstricted arteries. In concluding remarks, the authors stated:
Together, these data suggest that the cardiovascular system is indeed a valid therapeutic target for CBD.
A 2021 study on the therapeutic use of CBD to treat hypertensive rats yielded insights that may apply to human conditions. The authors wrote:
Our work is the first to show that CBD treatment has unique endothelial (vascular)-structure- and function-protective properties in hypertensive rats. We revealed that chronic treatment with CBD reduced hypertrophy and improved endothelium-dependent vasodilation.
And went on to explain:
Improvements in endothelial (vascular) function are important in the prevention and therapy of essential hypertension. Targeting the hypertension-associated adverse vascular changes by using CBD as an add-on therapy might represent a promising therapeutic strategy for patients with endothelial-dysfunction–associated diseases, in addition to achieving absolute reductions in blood pressure.
While CBD appears to have both neutral and potentially beneficial effects on heart health, the benefit-risk relationship of THC is less well-defined. A study published in Future Cardiology reported that oral treatment with low-dose THC inhibits atherosclerosis progression in mice while noting that “these promising results are in conflict with the health risks of smoking marijuana.”
THC has been shown to produce an inflammation response to the endothelial cells that line the interior of blood vessels. Prolonged cellular inflammation can lead to constriction of the vessels and increase the risk of arteriosclerosis.
CannaMD has noted this phenomenon in a prior post titled “Marijuana & Heart Disease: Natural Supplement May Mitigate Risk.”
The article included findings from a 2022 study conducted by a research team at Stanford University. Researchers found that under laboratory conditions genistein, which is a naturally occurring compound found in soybeans and fava beans, blocked the THC-induced inflammation of endothelial cells and reduced atherosclerotic plaque in mice. This led the authors to state:
Collectively, these results indicated that genistein could reverse delta-9-THC-induced effects [on the cardiovascular system].
It should be noted that these findings, while promising, are preliminary and have not yet been replicated in human subjects. At this time, CannaMD‘s medical professionals are not in a position to formally recommend the consumption of genistein via soybeans or fava beans and would caution medical marijuana patients against assuming that genistein supplementation represents a panacea for THC exposure. As more information becomes available, we will continue to provide updates on the possible therapeutic benefits identified in this first-of-its-kind research.
Talk to a Marijuana Doctor
If you have questions about medical marijuana or want to qualify to purchase legal cannabis products, CannaMD‘s state-certified medical marijuana doctors are here to help! Contact us at (855) 420-9170. Find out if you qualify for medical marijuana treatment with our quick online application!