In August of 2020, the American Heart Association (AHA) released a position paper titled “Medical Marijuana, Recreational Cannabis, and Cardiovascular Health: A Scientific Statement From the American Heart Association.” This comprehensive document includes both a general summary of current research on cannabis use and more specific findings on its role in cardiovascular health and health risks. The full text is available in the peer-reviewed journal, Circulation.
As Florida’s leading medical marijuana physicians, CannaMD has summarized the full AHA statement below, with an emphasis on the material most relevant to cardiac health. Little time will be devoted to opening sections which cover well-documented topics such as historic and current cannabis use, definitions, formulations, pharmacokinetics, pharmacodynamics, and policies on use. Beginning with the subsection on “Dosing Recommendations,” this summary will then follow the body of the statement, addressing each subsection in turn.
To achieve therapeutic benefits while avoiding adverse effects, the AHA recommends a gradual approach to dosing, noting that dosing with smoked or vaporized cannabis is a variable process influenced by the potency of the product, its processing, and differences in smoking and vaporizing techniques. Their recommendation is that:
Dosing should begin at the lowest possible dose, be increased gradually with caution, and with sufficient time between puffs/inhalations to gauge effects, and cease with the onset of disorientation, dizziness, ataxia, agitation, anxiety, tachycardia and orthostatic hypotension, depression, hallucinations, or psychosis.
Noting that the effects of oral administration of cannabis (edibles) can be less predictable that smoked or vaporized administration of products with similar levels of specific cannabinoids, the AHA cautions:
Patients must be made aware that the onset of effects begins within 30 minutes to ≥1 hour after ingestion with a peak effect within 3 to 4 hours; thus, they should be particularly careful about stacking oral doses. Consumption of edibles should proceed slowly and in small quantities at a time with sufficient time between doses. Administration with a high-fat meal significantly increases the absorption of oral cannabinoid and may exacerbate these effects.
Cannabis: Potential And Known Benefits
The AHA statement acknowledges a number of known therapeutic effects of marijuana use, including pain modulation, cachexia (extreme weight loss), nausea/vomiting, and spasticity. The authors also list a range of additional conditions for which there are possible benefits of cannabis therapies, including opiate withdraw, dystonia, glaucoma, Alzheimer’s disease, anxiety and depression, anti-tumor effects, inflammatory bowel diseases, Parkinson’s disease, and sleep disorders. Thirdly, the statement notes that there are currently no “well documented” cardiovascular benefits of cannabis.
The AHA position paper then moves on to address a range of known, potential, and suggested safety concerns associated with cannabis use.
Acute Effects Of Marijuana
The authors note a range of short-term effects of cannabis consumption, most of which are well known and documented. These include ocular blurred vision, altered judgment, euphoria, and impaired motor coordination, along with instances of anxiety, paranoia, and psychosis with higher doses. They also reference some specific cardiovascular effects that can include an elevated heart rate and irregular heartbeat, but do not detail potential risks associated with these conditions, or user groups that might be most affected. Based on existing guidelines, the authors note:
Because of the increased systemic absorption, slower time to onset, and peak effect compared with smoked cannabis, edible consumption appears more likely to result in adverse effects, particularly psychiatric and cardiovascular.
Cardiac And Vascular Effects
Cannabis is known to produce a range of cardiovascular effects. THC stimulates the sympathetic nervous system, which controls the body’s heightened response to danger or threat, while inhibiting the parasympathetic nervous system, which promotes rest and digestion. In contrast, CBD reduces heart rate and blood pressure, improves vasodilation, and reduces inflammation. The authors do note that “compared with smoking tobacco, smoking and inhaling cannabis regardless of THC content has been shown to increase the concentrations of blood carboxyhemoglobin 5-fold with a 3-fold increase in tar.” (Worth noting: The cited study was conducted in 1988 and funded through a grant by the National Institute on Drug Abuse. Mounting evidence has since suggested that marijuana use is “not associated with adverse effects on pulmonary function” or lung cancer.)
When administering smoked or vaped cannabis, carbon monoxide intoxication may occur depending on the depth of inhalation and length of breath holding, resulting in the increased oxidation of lipoproteins, impaired oxygen binding and certain cardiac concerns. Perhaps the takeaway from this last concern is to limit the depth and duration of inhalation when dosing with smoked or vaped marijuana.
The AHA statement raises questions on whether cannabis use plays a role in major cardiac events such as arrhythmia and heart attacks, but does not draw any definitive conclusions. Reasons for this uncertainty are said to include the limited number of long-term and unbiased studies, and the lack of dose or product standardization among cannabis users.
The authors summarize that “many epidemiological studies may be confounded by factors associated with access to health care and other adverse health behaviors such as tobacco use,” and add that “because the concentration of THC in cannabis has been increasing over the past several years, earlier studies may not be relevant to the present experience.”
Citing one of the most extensive studies to date on the long-term effects of coronary risk, the AHA states:
Cumulative lifetime and recent cannabis use did not show an association with incidence of cardiovascular disease, coronary heart disease, or cardiac mortality. However, several studies have shown signals for adverse cardiac outcomes, mostly for hospitalized patients with inherent selection bias. In the case of studies including only participants who were hospitalized, only a fraction of the overall population who experienced a health outcome were analyzed. Of note, when hospitalized patients with cannabis use serve as cases and those without cannabis use serve as controls, a high probability of selection bias exists. Thus, uncertainty exists for cannabis use as a cause for hospitalization.
The authors note a study that reports a small increase in cardiac-related mortality (2.3% for men, 1.3% for women) in states that legalized medical cannabis programs, and a possible relationship between cannabis use and atrial fibrillation, while also noting that data and statistical adjustment from this and similar studies may have failed to take into account concomitant use of tobacco or other drugs. Also mentioned was an Australian study that showed an increased risk of stroke for heavy cannabis users, but no increased risk among moderate to infrequent users.
A study suggesting a link between smoked cannabis and arteritis was mentioned, with the notation that conclusions from this study were inconclusive due to the fact that 97% of study participants also smoked tobacco. Based on the numerous variables and unknown factors present in many of the cited studies, and on the relative scarcity of relevant long-term studies, the authors summed up the AHA’s opinion with the statement that:
Overall, 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.
Smoking And Vaping Marijuana: Concerns
After noting that “cannabis smoke contains many of the same carcinogens and mutagens as tobacco smoke,” the statement went on to conclude that:
Limited and conflicting evidence from epidemiological studies has not shown a robust and consistent association between cannabis use and various types of cancer.
There was a mention of “low-strength” evidence suggesting long-term smoking of marijuana may be associated with testicular cancer, while associations with lung cancer were “mixed and confounded by few marijuana-only smokers, poor exposure assessment, and inadequate adjustment within studies.”
More insights on the subject come from a 2005 study that states:
Both [tobacco and marijuana] smoke contain carcinogens and particulate matter that promotes inflammatory immune responses that may enhance the carcinogenic effects of the smoke. However, cannabis typically down-regulates immunologically-generated free radical production by promoting a Th2 immune cytokine profile.
Furthermore, THC inhibits the enzyme necessary to activate some of the carcinogens found in smoke. In contrast, tobacco smoke increases the likelihood of carcinogenesis by overcoming normal cellular checkpoint protective mechanisms through the activity of respiratory epithelial cell nicotine receptors.
The AHA statement notes health concerns associated with the consumption of synthetic, illicit products laced with brodifacoum, and the health issue known as e-cigarette or vaping product use-associated lung injury (EVALI), which has been linked to vitamin E acetate compounds found in some vaping products. (Note: Florida medical marijuana products do not contain vitamin E acetate.)
The authors also caution against the consumption of certain over-the-counter topical CBD products which do not fall under the U.S. Food and Drug Administration (FDA) regulatory oversight guidance, warning that “the potential exists for these products to contain impurities such as heavy metals, herbicides, pesticides, and fungicides.”
Marijuana Side Effects, Addiction, And Drug Interactions
Three areas of potential concern noted in the AHA’s statement are worthy of a brief review. Among these are chronic side effects that include the increased risk long-term cannabis use may pose for certain individuals with a predisposition for psychosis and schizophrenia. Also mentioned are the issues long-term cannabis users may experience on cessation of use. These can include anxiety, irritability, depression, sleep disorders, and headaches. Such symptoms are reported to peak around ten days after cessation, and resolve within 30 days.
Addiction concerns for cannabis use disorder were also noted, though the exact level of risk was not well identified, with one study placing the risk of developing the disorder between 10 and 30 percent. Different numbers come from another study which surveyed long-term users who reported more than 200 days per year of cannabis use. The study concluded that the prevalences of 12-month and lifetime manifestations of cannabis use disorder were 2.5% and 6.3% respectively.
A third area of concern noted was the possibility of drug-drug interactions. The authors stated:
Drug interactions with cannabis can be expected to vary considerably in clinical significance given the wide variability in products, potencies, ratios of THC and CBD, doses, routes of administration, and populations using cannabinoids.
A list of specific known interactions was embedded in the manuscript in table form, and can be studied for specifics.
Considerations For Special Populations
The AHA statement identifies several user groups that may have additional concerns related to marijuana use.
YOUNG ADULTS: A commonly cited concern that is echoed by the AHA is the early adoption of cannabis, which is defined as use before 16 to 18 years of age. The statement references a number of studies that suggest potential behavioral and developmental issues associated with marijuana use during adolescence and teen years, but also notes that many of these studies failed to take genetic, environmental, and other factors into account. More insights on the subject can be found on our blog: Marijuana and IQ: What Do We Know For Sure?.
A more definitive warning in the same section of the statement cites a study reporting higher odds of stroke in young marijuana users as compared to non-users, with the greatest risk associated with heavy use.
PREGNANT WOMEN: Marijuana use during pregnancy remains a controversial subject, and the AHA statement raises the possibility of risks including low birth weight, anemia, and brain development, before going on to note that:
[A] lack of definitive evidence has resulted in insufficient information on the health implications of cannabis use […] The American College of Obstetricians and Gynecologists holds that women who are pregnant or contemplating pregnancy should be encouraged to discontinue marijuana use.
For a more detailed look at the current state of research on the subject, refer to CannaMD‘s article: Marijuana & Pregnancy: Top Studies.
GERIATRIC POPULATION: The AHA acknowledges that cannabis therapies have been suggested as a safe and effective alternative for older adults seeking a reduction in neuropathic pain, improved quality of life, and decreased prescription drug use. A cited study indicated that adults over 50 who continued to use cannabis were at an elevated risk of developing substance disorders as compared to former users, but were not at greater risk of mental disorders.
Also mentioned was the finding that older individuals in general experienced lesser effects from a given dose of cannabis as compared to younger users. The authors of that study noted:
Overall, the pharmacodynamic effects of THC were smaller than effects previously reported in young adults. In conclusion, THC appeared to be safe and well tolerated by healthy older individuals.
An additional concern noted in the statement was the risk of drug-drug interactions in an older population that was more likely to be taking prescription medications.
TRANSPLANT PATIENTS: After noting that most organ transplant programs do not recommend patients with active drug or alcohol abuse undergo transplantation, the authors note that legislation in a number of states prohibits denial of transplants on this basis. A survey by the AHA revealed that a majority of respondents supported transplantation listing for patients who use legal medical cannabis, but far fewer supported the same listing for individuals using recreational marijuana. The AHA recommends the cessation of cannabis use before transplantation, in particular noting the pulmonary risks inhaled cannabis poses for compromised immune systems.
COMORBID CARDIOVASCULAR DISEASE: The position statement authors warn that:
Because cannabis consumption increases myocardial oxygen demand and decreases myocardial oxygen supply, patients with underlying ischemic disease could see an increase in angina, particularly when cannabis is smoked.
Based on data from a 2020 study, it is estimated that 2 million of the 89.6 million adults who reported marijuana use had cardiovascular disease; however, the AHA notes that current observational studies have not made a definitive link between cannabis use and an increased risk of heart attacks. The authors referenced several studies that point to increased mortality risks for cannabis users suffering from cardiovascular diseases, and raised questions on the increased risks of cerebrovascular accidents among users. Other studies cited showed mixed cardiovascular markers for cannabis-using patients with coronary artery disease and angina, with some documenting a decrease in onset of angina during exercise, and others showing decreased end-diastolic volume, stroke index, and ejection fraction without causing any change in end-systolic volume or cardiac index.
PATIENTS WITH CARDIAC RISK FACTORS: After citing a study that showed continued use of cannabis to be associated with an increased risk of developing metabolic syndrome, the authors went on to note that:
[As compared to non-users] those who use cannabis had a similar or reduced incidence of hyperglycemia, elevated fasting blood glucose, and diabetes mellitus, as well as a lower body mass index, total cholesterol, and low-density lipoprotein.
A study indicating an increased risk of stroke among younger and frequent marijuana smokers noted the potential role of concomitant cigarette and e-cigarette use, stating:
Marijuana users were more often current combustible cigarette users, current e-cigarette users , and heavy alcohol drinkers when compared with nonusers. However, diabetes mellitus, hypertension, and hypercholesterolemia were less frequently observed among marijuana users.
Patient Education And Considerations
In the concluding section of the AHA statement paper, the authors recommend that:
The decision to use cannabis, whether medicinal or recreational, should involve shared decision-making between provider and patient, highlighting possible risks and benefits for various forms of administration, and adverse effects.
They also caution:
Because of the risk of contamination and adulteration, all cannabis products on the black or gray market, especially synthetic illicit cannabinoids, should be avoided.
The statement then concludes with a listing of the AHA’s recommendations for policy considerations, future directions for research, and the need for education on the effects, potential benefits, and risk of cannabis use.