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One of the most widely known risks linked to the COVID-19 vaccine is myocarditis, especially in young males — and now a new Stanford study has shed some light on why this rare effect can occur.

Myocarditis, which is inflammation of the heart, occurs in about one in 140,000 people who receive the first dose of the vaccine and one in 32,000 after the second dose, according to a Stanford press release. Among males 30 and younger, that rises to one in 16,750.

Symptoms of the condition include chest pain, shortness of breath, fever and palpitations, which can occur just one to three days after vaccination. Another marker is heightened levels of cardiac troponin, which indicates that the heart muscle has been damaged.

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In most cases, people who experience myocarditis recover quickly and restore full heart function, according to study author Joseph Wu, MD, PhD, the director of the Stanford Cardiovascular Institute and a professor of medicine and radiology.

“It’s not a heart attack in the traditional sense,” Wu told Fox News Digital. “There’s no blockage of blood vessels as found in most common heart attacks. When symptoms are mild and the inflammation hasn’t caused structural damage to the heart, we just observe these patients to make sure they recover.”

In rare cases, however, severe heart inflammation can lead to hospitalizations, critical illness or death, Wu noted.

Finding the cause

The new Stanford study — conducted in collaboration with The Ohio State University — aimed to determine the reasons for the myocarditis. The research team analyzed blood samples from vaccinated people, some with myocarditis and some without. 

They found that those with myocarditis had two proteins in their blood, CXCL10 and IFN-gamma, which are released by immune cells. Those proteins then activate more inflammation.

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“We think these two are the major drivers of myocarditis,” said Wu. “Your body needs these cytokines to ward off viruses. It’s essential to immune response, but can become toxic in large amounts.”

In mouse and heart tissue models, high levels of these proteins led to signs of heart irritation, similar to mild myocarditis.

Prevention mechanism

“One of the most striking findings was how much we could reduce heart damage in our models by specifically blocking these two cytokines, without shutting down the entire (desired) immune response to the vaccine,” Wu told Fox News Digital, noting that a targeted, “fine‑tuning” immune approach might be enough to protect the heart.

“This points to a possible future way to prevent or treat myocarditis in people who are at the highest risk, while keeping the benefits of vaccination,” he added.

The team also found that genistein, an estrogen-like natural compound found in soybeans, reduced inflammation in lab tests, but this has not yet been tested in humans.

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The findings were published in the journal Science Translational Medicine.

“This is a very complex study,” Fox News senior medical analyst Dr. Marc Siegel told Fox News Digital. “Myocarditis is very rare, and the immune mechanism makes sense.”

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“Myocarditis is worse with COVID — much more common, and generally much more severe.” 

Wu agreed, adding that COVID infection is about 10 times more likely to cause myocarditis compared to mRNA-based vaccines.

‘Crucial tool’

The researchers emphasized that COVID-19 vaccines have been “heavily scrutinized” for safety and have been shown to have an “excellent safety record.”

“mRNA vaccines remain a crucial tool against COVID‑19, and this research helps explain a rare side effect and suggests ways to make future vaccines even safer, rather than a reason to avoid vaccination,” Wu said.

“The overall benefits of COVID‑19 vaccination still clearly outweigh the small risk of myocarditis for nearly all groups.”

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The study did have some limitations, primarily the fact that most of the data came from experimental systems (mice and human cells in the lab), which cannot fully capture how myocarditis develops and resolves in real patients, according to Wu.

“This points to a possible future way to prevent or treat myocarditis in people who are at the highest risk.”

“These findings do not change what people should do right now, because our work is still at the preclinical (mouse and human cells) stage,” he said. “Clinical studies will be needed to confirm whether targeted treatments are safe and effective.”

The researcher also added that myocarditis risk could rise with other types of vaccines.

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“Other vaccines can cause myocarditis and inflammatory problems, but the symptoms tend to be more diffuse,” he said in the release. “Plus, mRNA-based COVID-19 vaccines’ risks have received intense public scrutiny and media coverage. If you get chest pains from a COVID vaccine, you go to the hospital to get checked out, and if the serum troponin is positive, then you get diagnosed with myocarditis. If you get achy muscles or joints from a flu vaccine, you just blow it off.”

The study was funded by the National Institutes of Health and the Gootter-Jensen Foundation.

Cannabis has been linked to some significant medical benefits, but recent research calls those into question.

A major new analysis published in JAMA examined more than 2,500 scientific papers from the last 15 years, including other reviews, clinical trials and guidelines focused on medical marijuana.

“While many people turn to cannabis seeking relief, our review highlights significant gaps between public perception and scientific evidence regarding its effectiveness for most medical conditions,” Dr. Michael Hsu of University of California – Los Angeles (UCLA) Health Sciences, author of the study, said in a press release.

The researchers — led by UCLA with contributions from Harvard, UC San Francisco, Washington University School of Medicine and New York University — set out to determine how strong the research is on the effectiveness of medical cannabis and to offer evidence-based clinical guidance.

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The review found that evidence supporting most medical uses of cannabis or cannabinoids is limited or insufficient, the release stated.

“Whenever a substance is widely used, there is likely to be a very wide set of outcomes,” Alex Dimitriu, MD, double board-certified in Psychiatry and Sleep Medicine and founder of Menlo Park Psychiatry & Sleep Medicine, told Fox News Digital. 

“Cannabis is now used by about 15 to 25% of U.S. adults in the past year, for various reasons ranging from recreational to medicinal. This study points to the reality that this widely used substance is not a panacea,” said Dimitriu, who was not involved in the study.

There are very few conditions for which cannabinoid therapies have clear, well-established benefits backed by high-quality clinical data, according to the researchers.

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The strongest evidence supports FDA-approved cannabinoid medications for treating specific conditions, including HIV/AIDS-related appetite loss, chemotherapy-induced nausea and vomiting, and certain severe pediatric seizure disorders.

For many other conditions that are commonly treated with cannabis — such as chronic pain, insomnia, anxiety or post-traumatic stress disorder — evidence from randomized trials did not support meaningful benefit.

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The analysis also examined safety concerns — in particular, how young people using high-potency cannabis may be more likely to suffer higher rates of psychotic symptoms and anxiety disorder.

Daily inhaled cannabis use was also linked to increased risks of coronary heart disease, myocardial infarction (heart attack) and stroke when compared with non-daily use.

Based on these findings, the review emphasizes that clinicians should weigh potential benefits against known risks when discussing cannabis with patients.

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The authors suggest that clinicians screen patients for cardiovascular risk, evaluate mental health history, check for possible drug interactions and consider conditions where risks may outweigh benefits.

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They recommend open, realistic conversations and caution against assuming that cannabis is broadly effective for medical conditions.

“Patients deserve honest conversations about what the science does and doesn’t tell us about medical cannabis,” Hsu said.

This article is a narrative review rather than a systematic review, so it did not use the strict, standardized methods that help reduce bias in how studies are selected and evaluated, the researchers noted.

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The review notes further limitations, including that some evidence comes from observational research rather than randomized trials, which means it cannot establish cause and effect.

The trial results also may not apply to all populations, products or doses.