We've accepted Wegovy and Zepbound. The next phase is harder.

This time last year, people were still bickering about whether Novo Nordisk’s Wegovy and Eli Lilly & Co.’s Zepbound represented a shortcut to losing weight or a medical breakthrough. But with reams of data on the drugs’ health benefits beyond reducing obesity — including mitigating heart disease, diabetes, chronic kidney disease, and sleep apnea — most seem to have finally accepted their potentially immense societal value.

Now comes the hard part. These highly effective drugs — GLP-1s — are changing the way obesity is viewed and treated. The changes are coming so fast and could benefit so many that they’ve created new questions and ethical quandaries for medical professionals, including who should get them.

The theoretical market for Wegovy and Zepbound is massive: The Food and Drug Administration approved them for anyone with a body mass index of 30 or more — 27 or higher for individuals with a weight-related condition like high blood pressure or sleep apnea. Some 57 million working-age Americans with private insurance match those criteria, as do nearly 14 million retirement-age Americans. The expectation is that once started, the drugs will need to be taken for life to maintain the results.

But does everybody who fits that broad description need the drugs? Opinions among physicians vary. Some feel strongly that everyone deserves treatment, while others draw a distinction between people at risk of or already experiencing weight-related health complications and those who are perfectly healthy at a BMI that would make them eligible for the drugs.

Within both camps, shortages and the drugs’ high prices are forcing doctors to come up with ways of prioritizing which patients should get them. That’s both a necessary response to an ongoing problem and forward-thinking, says Robert Kushner, who specializes in obesity medicine at Northwestern University’s Feinberg School of Medicine. "Are we going to put this in the water? Are we going to treat everyone with obesity? How do we utilize this effective tool to get it into the arms of people who need it most?"

The field needs an evidence-backed approach to help better define who the right candidate is for GLP-1s. To that end, an international committee of obesity experts will release an interim report in early 2025 that lays out criteria for diagnosing "clinical" obesity or where excess weight is causing or raising the risk of other health problems. Ideally, that will help doctors more easily distinguish between "who has the true disease of obesity, who we need to treat early," and the people who gained 10 or 20 pounds and crossed the BMI threshold into obesity yet are still perfectly healthy, says Kushner, who led the commission.

Those definitions will surely rankle some Americans — and their doctors. No one wants even more gatekeeping at a time when so many can’t find or afford these medications. But they could also be a good step toward a more critical assessment of the connection between weight and health -one that could make it easier and more equitable for those most in need to get the drugs and offer insurers guidelines for facilitating their coverage.

And maybe that will help resolve tensions between doctors and insurers. Obesity specialists have countless infuriating stories of patients losing coverage for GLP-1s once their BMI drops below a certain number. The reality is without ongoing treatment, the weight will come back — and with it, so will their patients’ risks of conditions like diabetes and high blood pressure. Coming up with a way to define obesity that centers on the risk of disease might clarify the need for long-term treatment.

That could also help doctors as they try to answer another important question: When is someone’s weight loss enough?

Not long ago, obesity doctors spent most of their time urging their patients to keep going — that if they could stick with their lifestyle changes, health benefits were within reach. "I spend more of my time trying to convince people to stop losing weight," Louis Aronne, an obesity expert at Weill Cornell Medicine in New York, said during a keynote speech at a recent obesity medicine conference.

The worry is that these drugs not only cause someone to lose fat but muscle, too, and that they can affect nutrient intake. All of that must factor into the patient’s weight loss journey.

But doctors still lack a consensus on the right way to manage a patient’s obesity using drugs. Should they aim for a specific BMI range (widely considered a problematic metric) or look at waist-to-height ratio (an assessment of body fat distribution, which is linked to heart disease risk)? Or should they aim for specific health markers, like lower blood sugar levels or cholesterol? How much should they factor in muscle mass and nutrient loss during treatment? Complicating all of this is the question of GLP-1’s broader health benefits, some of which accrue regardless of the magnitude of weight loss.

The need to establish goals isn’t unusual. Transformative treatments for chronic disease have a way of setting standards for what doctors consider healthy. The advent of drugs for lowering cholesterol and blood pressure and treating diabetes enabled doctors to define watermarks for treatment. The difference with obesity drugs, though, is patients tend to have strong opinions on those goals, and they might not match what the data (or their doctor) says is best.

"These are small issues now, but I think they are going to get bigger as time goes on. We need to be paying attention," Aronne said.

Eventually, data will be the best guide. But until then, doctors will keep feeling their way through this new era.

Lisa Jarvis is a Bloomberg Opinion columnist covering biotech, health care and the pharmaceutical industry. Previously, she was executive editor of Chemical & Engineering News.