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By Nick Mordowanec
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New research finds that regular marijuana use, including both smoking and THC-laced edibles, is linked to early warning signs of cardiovascular disease.
Why It Matters
The growing legalization and widespread use of marijuana in the United States has sparked concerns about short- and long-term potential health impacts. New studies such as this indicate a measurable risk of cardiovascular problems for young and otherwise healthy marijuana users, suggesting that marijuana use could have dubious health outcomes.
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What To Know
The study, by lead author Leila Mohammadi at the University of California, San Francisco (UCSF) and senior author Matthew Springer at UCSF, and published in the peer-reviewed medical journal JAMA Cardiology, examined the potential connection between THC smoking and ingestion, and endothelial dysfunction—where the inner lining of blood vessels, the endothelium, is unable to function properly and could lead to an array of cardiovascular problems, per The Cleveland Clinic.
Springer said the study emanated from research several decades ago showing that chronic tobacco smokers had poor endothelial function, even if they had not smoked recently, and so did non-smokers who were frequently exposed to secondhand smoke. Endothelial dysfunction, even in otherwise outwardly healthy people, is an indication of unhealthy arteries and increased risk of cardiovascular disease later in life, he said, wondering if it could be true in marijuana consumers as well since both kinds of smoke included the thousands of chemicals that resulted from burning plant material.
"A number of years ago, we developed a way to study changes in endothelial function in rats, using a technique very similar to how we measure it in humans, and we saw that, as in humans, even brief exposures to secondhand smoke from tobacco impaired vascular function in the rats," Springer told Newsweek. "We subsequently showed that brief exposures to secondhand smoke from marijuana, and active smoking of marijuana, similarly impaired vascular function in the rats, even if the smoke was from marijuana lacking THC and the other cannabinoids."
This cross-sectional study of 55 participants discovered that vascular endothelial function was impaired in both chronic marijuana smokers and tetrahydrocannabinol (THC) edible users, whereas serum from marijuana smokers but not THC-edible users blunted nitric oxide production in cultured endothelial cells.
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"In other words, the blood vessels don't seem to care if the smoke is from tobacco or marijuana," he said.
Such findings could challenge previous assumptions that marijuana is a benign alternative to tobacco.
Early Cardiovascular Signs Detected
The study divided the participants into three groups: marijuana smokers, THC-edible users, and nonusers. Researchers observed that marijuana smokers showed a 42 percent reduction in vascular function, while THC-edible users experienced a 56 percent reduction compared to those who did not use marijuana.
Heart Attack, Stroke and Death Risks
A retrospective analysis of over 4.6 million people under age 50, published in March in JACC Advances, revealed that marijuana users faced a more than sixfold increased risk of heart attack, a fourfold risk of ischemic stroke, and a threefold risk of cardiovascular death, heart attack, or stroke, compared to non-users.
Meta-Analysis Confirms Higher Heart Attack Risk
A meta-analysis presented to the American College of Cardiology pooled data from 12 studies involving 75 million people. The association between marijuana use and heart attack was positive, with current users being 1.5 times more likely to suffer a heart attack than nonusers, according to SciTechDaily.
Associations, Not Direct Causes
Scientists cautioned that these findings show strong associations but do not definitively prove marijuana or THC causes vascular damage or heart attacks.
Springer said they saw that the marijuana smokers exhibited changes in their blood serum relevant to endothelial dysfunction but that THC edible users did not. We know that tobacco smoke has this effect in humans and marijuana smoke lacking THC has this effect in rats, he said, so it's likely that the smoked marijuana and the ingested THC both lead to endothelial dysfunction for different reasons.
He said there was a correlation between how strongly vascular function was impaired, and the number of smoking sessions per week or amount of edible THC ingested per week. The study intentionally looked at people who used these products at a relatively high usage level, to ensure that they did not miss a relationship.
However, the study's results only suggest that marijuana smoking and ingestion of THC cause poor vascular function.
"The consequences for individuals and widespread are that people who decide to smoke marijuana or use THC edibles should be aware that, at least at the relatively high usage in our study, neither of those behaviors should be considered harmless," Springer said. "The widespread consequences relate to clean air laws and involuntary exposure to secondhand smoke: in my opinion, smoking cannabis should not be allowed where smoking tobacco is not allowed."
Confounding factors like concurrent use of other drugs were ruled out in the UCSF study by questionnaires followed by drug testing.
Based on these results, researchers urged clinicians to ask patients about marijuana use during cardiovascular risk assessments. Dr. Ibrahim Kamel, lead author of the retrospective study, said, "At a policy level, a fair warning should be made so that the people who are consuming cannabis know that there are risks," according to SciTechDaily on March 18.
What People Are Saying
Matthew Springer to Newsweek: "I feel that our succession of studies over the years in rats and now in humans has at least put to rest the concept that marijuana is harmless. How harmful it is, is debatable. But the public (and the medical field) should view cannabis and THC iteself as product that are not without health risk. THC seems to have some beneficial effects also, so there needs to be a balance between risk and benefit that is best decided with both eyes open."
Dr. Ibrahim Kamel, clinical instructor at Boston University and internal medicine resident at St. Elizabeth Medical Center, told SciTechDaily in March: "Asking about cannabis use should be part of clinicians' workup to understand patients' overall cardiovascular risk, similar to asking about smoking cigarettes...a fair warning should be made so that the people who are consuming cannabis know that there are risks."
Dr. Andrew Freeman, director of cardiovascular prevention and wellness at National Jewish Health in Denver, told CNN: "Could it be that other forms of marijuana — teas, tinctures, edibles — are perhaps not as benign as we once thought?"
What Happens Next
Researchers have called for larger, long-term studies to more conclusively determine the direct effects of marijuana and THC products on cardiovascular health and to identify safe usage levels, if any. Future policy guidance and clinical recommendations may be updated in light of further research outcomes.
Updated 5/29/25, 10:08 a.m. ET: This story was updated with remarks from Matthew Springer.
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