The heart of the question: Who can get Medicare-covered weight loss medicine?

But exactly what level of cardiovascular risk should make someone eligible for such coverage, how many people could become eligible, and what could it cost the nation?

A new study dives into these questions. It finds a wide range of answers that differ by millions of people and billions of dollars, depending on how private insurance plans that contract with Medicare are potentially allowed to proceed.

As many as 3.6 million people are most likely to qualify. This assumes plans only allow people with obesity who have already had a heart attack or stroke, or gotten diagnosed with coronary artery disease or angina, to get coverage for semaglutide injections, the study suggests.

That number doesn't include the 7 million who may already qualify because they have diabetes plus obesity.

The study was led by Alexander Chaitoff, M.D., M.P.H., a VA Ann Arbor Healthcare System and University of Michigan Medical School researcher, and published in the Annals of Internal Medicine.

But what about older people with obesity who don't have diabetes and haven't yet had a major cardiovascular diagnosis, but have elevated odds of a heart attack or stroke in the next 10 years?

If prescription drug coverage plans allow those with the highest cardiovascular risk scores to get full or partial coverage of the cost of semaglutide, another 5.1 million Americans could qualify the study finds. And if plans allow people with intermediate risk to qualify for coverage, another 6.5 million people could be eligible.

Medicare coverage of semaglutide -- but for whom?

Chaitoff and his former colleagues at Harvard University launched the study after the announcement this spring that Medicare would allow coverage of semaglutide for enrollees in drug plans if they had established cardiovascular disease. The drug is sold as Wegovy when used for weight loss, and Ozempic when used for diabetes.

Without a specific definition from Medicare of what constitutes "established cardiovascular disease," Chaitoff said, "it's unclear of exactly who will quality now, who may qualify in the future, and if certain high-risk people will be left out."

Medicare plans may be more likely to go with the short list of diagnoses that people had to have in order to qualify for the clinical trial that led to semaglutide's approval for cardiovascular disease and obesity.

But they could potentially take more of a preventive approach -- like they do with many medications that reduce the risk that someone will have a heart attack or a stroke.

Chaitoff, who provides primary care to veterans at VAAAHS, notes that Medicare Part D and Medicare Advantage plans could opt to set conditions to determine which high-risk patients could qualify for treatment with semaglutide. They could also tell them to share more of the cost.

He notes that veterans with obesity and at least one obesity-related condition can qualify for Wegovy coverage from the Veterans Health Administration if they participate in the MOVE weight management program over months or years.

But for everyone else over age 65, it's up to the plan that they've chosen during Medicare Open Enrollment to provide their prescription drug coverage.

"If those plans focus on coverage for people with the same conditions as in the clinical trial, 1 in 7 Medicare participants with obesity would now have access, which is an important expansion," said Chaitoff. "However, the other 6 of the 7 would not, and most of them also have an elevated cardiovascular risk based on their overall health status."

Risk scoring for future cardiovascular disease

The researchers used data from the National Health and Nutrition Examination Survey, conducted in samples of the United States public every year. This allowed them to calculate cardiovascular risk scores for every Medicare-enrolled person with a body mass index of 27 kg/m2 and above who didn't already have a history of heart attack, stroke, coronary artery disease or angina.

The scoring tool is called the ASCVD, and incorporates many factors to help guide clinicians who are trying to decide what preventive treatments a person might need. Those who score 20% or above are considered high risk for heart disease or stroke, while those who score 7.5% to just under 20% are considered intermediate risk.

Chaitoff notes that people who score above 20% should get immediate treatment to reduce their risk -- which typically includes drugs to reduce blood pressure, cholesterol, and even potentially pre-diabetic elevated blood sugar levels, as well as help with quitting tobacco, increasing physical activity, improving diet and losing weight as necessary.

In fact, he says, this is the same approach used in those who have survived a heart attack or stroke, or gotten a diagnosis of CAD or angina.

But those with scores between 7.5% and 20% also should get help reducing the risk factors that affect their score, which often includes medication.

"In practice, the way we treat both groups of people with elevated risk scores is not dissimilar -- we're making medical management decisions and lifestyle recommendations to prevent a future incident," Chaitoff explained. "Weight loss is listed in clinical guidelines as recommended for both groups, because of the general link between obesity and cardiovascular risk. But the only way Medicare will allow coverage of weight loss medication may have nothing to do with risk, only past diagnosis."

Coverage of medications that have been shown to lead to sustained weight loss -- as multiple medications including semaglutide have been -- would enable more people with obesity and elevated cardiovascular risk to achieve the goals set out in clinical guidelines, he added.

"Ultimately we need to ask ourselves, what level of evidence are we requiring for coverage of certain drugs, compared with the level of evidence that we require for coverage of other treatments," Chaitoff said. "With all that we know about obesity's impact on cardiovascular risk, it may be best to accept that a surrogate outcome of sustained reduction in weight is reasonable enough evidence for coverage. We do that for other conditions, but not obesity, and the questions are, why and is it appropriate."

Potential costs to Medicare

Semaglutide costs for Medicare plans will likely be the target of negotiations between the Centers for Medicare and Medicaid Services and the manufacturer of FDA-approved versions of the drug. But the price that is reached in those negotiations will only take effect the following year.

In the meantime, if only those with a history of heart attack or stroke are allowed to get it under the non-diabetes approval, and only 30% of them start the drug and stay on it for a year, the cost to Medicare could top $10 billion at current prices, the researchers estimate.