The problem is daunting: Powerful but expensive new drugs could help many of the 100 million American adults who have obesity and alleviate a grave public health concern.

But how can the nation afford lifelong treatments for so many people, with sticker prices for each patient ranging from about $900 to $1,300 every four weeks?

Some researchers, like Dr. Walter C. Willett, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health, have warned that the drugs could add 50 percent to the country’s health care spending.

“You can see this ballooning completely out of control,” he said.

But there is one factor often left out of these discussions: The drugs’ list prices are generally very different from the net prices, which companies receive after making secret deals with health insurers or the intermediaries known as pharmacy benefit managers. Companies generally do not reveal net prices, but there are data sources that can be used to estimate them.

A recent paper published by the American Enterprise Institute revealed that the net prices for the new obesity drugs are just a fraction of the published annual list prices.

And while the drugs’ prices remain out of reach for many, economists anticipate they will soon be driven down. More than a dozen companies are developing obesity drugs. As they enter the market, greater choice is expected to make prices plummet, as has happened with other expensive drugs.

“My prediction is that as competition increases, prices will decrease accordingly,” said Jalpa Doshi, professor of medicine and director of the economics evaluation unit at the University of Pennsylvania.

For now, manufacturers are reaping the rewards of soaring demand.

Investors expect Novo Nordisk, the manufacturer of Wegovy, to earn $4 billion in revenue this year. The company’s other drug, Ozempic, is expected to bring in $11 billion. The drugs are driving such a bonanza that they account for almost all of the latest economic growth in Denmark, the home of Novo Nordisk.

Those revenues are based on the net prices.

For their analysis, Benedic N. Ippolito, an economist at the American Enterprise Institute, and Joseph F. Levy, a health economist at Johns Hopkins Bloomberg School of Public Health, relied on data from SSR Health, which uses company financial filings and estimates of the number of prescriptions filled.

The economists derived net prices by using data from SSR Health for the second quarter of 2022 through the first quarter of 2023. The exception is Mounjaro, made by Eli Lilly, for which only data from the first quarter of 2023 was available.

Net prices, the revenue divided by the number of prescriptions in their analysis, appear to be around $700 every four weeks for Wegovy, or about $650 less than the list price; about $300 for Ozempic, or nearly $650 less than the list price; and approximately $215 for Mounjaro, or about $800 less than its list price.

That means Wegovy’s net price is about half of its list price, Ozempic’s is nearly two-thirds lower and Mounjaro’s net price is nearly 80 percent lower than its list price.

Dr. Ippolito cautioned that because prices and prescriptions are in flux, these figures might change over time, but added that “these estimates give a good sense for the likely amount paid by many insurers and give a good sense for the amount of discounting going on.”

Pragya Kakani, an economist at Weill Cornell Medical College, analyzed similar data with similar results but was not involved in Dr. Ippolito and Dr. Levy’s research.

Craig Garthwaite, a health care economist at Northwestern University, is especially intrigued by the net prices of Ozempic and Mounjaro. Both are approved for people with diabetes but also cause weight loss. Wegovy, the same drug as Ozempic, is approved for weight loss. But the price of Ozempic is substantially lower than Wegovy’s price.

The reason may be that Ozempic has a direct competitor in Mounjaro.

But even Wegovy, which so far has the market for the new obesity drugs to itself, has an unexpectedly low net price, Amitabh Chandra, a health care economist at Harvard, said.

“One might have naïvely thought that these are new medicines that are in great demand, so rebates would be small to nil,” Dr. Chandra said.

“I was shocked,” he said, “by the extent of the rebates.”

One question looms, experts say: What is weight loss worth to patients and society?

Obesity itself is expensive because it increases the risk for expensive diseases like diabetes and heart disease. One study found that obesity was associated with $1,861 excess yearly health costs per person, accounting for $172.74 billion in annual extra costs.

The Institute for Clinical and Economic Review, an influential nonprofit group, asked about a year ago if the new weight-loss drugs are cost-effective, meaning that their value in terms of a better quality of life, a longer life and benefit to society exceeds their cost.

Wegovy, the group reported, was not cost-effective. But the institute relied on an early and less precise estimate of the drug’s net price.

When shown Wegovy’s estimated net price in the A.E.I. research, the group’s chief medical officer, Dr. David M. Rind, said that if the calculations were correct, Wegovy was cost-effective but “still poses major budget challenges.”

Dr. Willett, of Harvard, added in an interview: “I don’t think anyone can predict exactly where this will go because competition may reduce prices, and the uptake is still not clear, but the potential cost could go way beyond anything we have seen.”

Still, the expectation is that with less obesity, there will be fewer expensive obesity-related health problems, including type 2 diabetes.

Not only can diabetes lead to kidney failure, blindness and amputations, it also doubles the risk for heart attacks and strokes.

Patients may also get relief from the extreme social stigma and, often, self-loathing that accompanies obesity.

Until recently, the idea that treating obesity would reduce obesity-related health risks was based on anecdotes and correlations, not cause and effect.

Then in August Novo Nordisk announced the results of a large study, showing that Wegovy can reduce the risk of heart attacks, strokes, hospitalizations for heart failure and heart disease deaths by 20 percent.

That outcome alters the picture, Dr. Garthwaite said.

Some insurers do not cover drugs like Wegovy and may view obesity medications as vanity drugs. In response, some patients are suing their insurers.

With a cardiovascular benefit, he said, that rationale for not covering the drugs is “out the window.”

While the net prices of the drugs may be lower than expected, they remain too expensive for many potential patients.

Those on Medicare, for instance, have no insurance coverage for Wegovy because Medicare is prevented by law from covering weight-loss drugs. Few state Medicaid programs cover the drug.

And while Novo Nordisk says that 80 percent of private insurers cover Wegovy, the drug is not affordable for all insured patients.

Katherine Baicker, a health economist, provost at the University of Chicago and an Eli Lilly board member, said that cheaper health insurance includes co-pays and deductibles that often render Wegovy out of reach. Patients with low-premium plans offered through the Affordable Care Act would similarly be priced out.

Dr. Scott Ramsey, a health economist at Fred Hutchinson Cancer Center, worries that poorer patients, who are uninsured or whose insurance requires high co-pays, will be looking on longingly as wealthier patients get the drugs.

“We spent 15 years talking about the soaring cost of obesity to the health care system,” Dr. Garthwaite, the Northwestern economist, added. But with a way to cut that cost in reach, he said the attitude of some insurers seems to be, “we don’t want you to come up with a fix that costs money.”

Relief should be coming soon, health economists predict, with companies rushing to develop their own drugs. Competition may lead to lower prices.

That happened, for example, with drugs for hepatitis C. An effective cure for the liver disease initially cost as much as $84,000, leading to dire warnings that the cost would be comparable to “total spending in the United States on all drugs.”

The list price of the hepatitis C treatment plunged, as competitors entered the market. Pharmacy benefit managers, which negotiate with drug makers, had more leverage as companies competed. Net prices fell accordingly.

A similar scenario may play out with Wegovy, which “is riding the wave of not having any direct competition,” Dr. Doshi said. But that status will end soon.

A version of Mounjaro by Eli Lilly is expected to be approved this year for obesity — a potential opening for insurers to agree to cover Wegovy but not Mounjaro, for example, if Wegovy’s price were to be sufficiently reduced.

Dr. Ippolito added that with more than 70 obesity drugs in development, he expected that competition would only increase.

For now, although the price of the drugs is likely at its peak, Dr. Chandra, the Harvard health care economist, argued that it is imperative for access to the drugs to be increased, even if that imposes a cost to society.

The purpose of health insurance is not to save money, he said, but “to improve the quality of life, happiness and self-esteem.”