In December, the Food and Drug Administration approved a new anti-obesity drug, Saxenda, the fourth prescription drug the agency has given the green light to fight obesity since 2012. But even though two-thirds of adults are overweight or obese — and many may need help sticking to New Year’s weight-loss resolutions — there’s a good chance their insurer won’t cover Saxenda or other anti-obesity drugs.

The health benefits of using anti-obesity drugs to lose weight—improvements in blood sugar and risk factors for heart disease, among other things—may not be immediately apparent. “For things that are preventive in the long term, it makes plan sponsors think about their strategy,” says Dr. Steve Miller, the chief medical officer at Express Scripts, which manages the prescription drug benefits for thousands of companies. Companies with high turnover, for example, are less likely to cover the drugs, he says.

“Most health plans will cover things that have an immediate impact in that plan year,” Miller says.

Miller estimates that about a third of companies don’t cover anti-obesity drugs at all, a third cover all FDA-approved weight-loss drugs, and a third cover approved drugs, but with restrictions to limit their use. The Medicare prescription drug program specifically excludes coverage of anti-obesity drugs.

Part of the reluctance by Medicare and private insurers to cover weight-loss drugs stems from serious safety problems with diet drugs in the past, including the withdrawal in 1997 of fenfluramine, part of the fen-phen diet drug combination that was found to damage heart valves.

Back then, weight-loss drugs were often dismissed as cosmetic treatments. But as the link between obesity and increased risk for type 2 diabetes, heart disease, cancer and other serious medical problems has become clearer, prescription drugs are seen as having a role to play in addressing the obesity epidemic. Obesity accounts for 21 percent of annual medical costs in the United States, or $190 billion, according to a 2012 study published in the Journal of Health Economics.

The new approved drugs — Belviq, Qsymia, Contrave and Saxenda — work by suppressing appetite, among other things. Saxenda is a subcutaneous injection, the other three drugs are in pill form. They’re generally safer and have fewer side effects than older drugs. In conjunction with diet and exercise, people typically lose between 5 and 10 percent of their body weight, research shows, modest weight loss but sufficient to meaningfully improve health.

The drugs are generally recommended for people with a body mass index of 30 or higher, the threshold for obesity. They may also be appropriate for overweight people with BMIs in the high 20s if they have heart disease, diabetes or other conditions.

In 2013, the American Medical Association officially recognized obesity as a disease.

Nevertheless, “people still assume that obesity is simply a matter of bad choices,” says Ted Kyle, advocacy adviser for the Obesity Society, a research and education organization. “At least half of the risk of obesity is inherited,” he says.

Many people who take an anti-obesity drug will remain on it for the rest of their lives. That gives insurers pause, says Miller.

The potential cost to insurers could be enormous, he says.

Susan Pisano, a spokesperson for America’s Health Insurance Plans, a trade group, says the variability of insurer coverage of anti-obesity drugs “relates to issues of evidence of effectiveness and evidence of safety.”

In 2012, the U.S Preventive Services Task Force, a non-partisan group of medical experts who make recommendations about preventive care, declined to recommend prescription drugs for weight loss, noting a lack of long-term safety data, among other things. But its analysis was based on the older drugs orlistat, which is sold over the counter as Alli or in prescription form as Xenical, and metformin, a diabetes drug that has not been approved for weight loss but is sometimes prescribed for that by doctors.

The task force did recommend obesity screening for all adults and children over age 6, however, and recommended patients be referred to intensive diet and behavioral modification interventions.

Under the health law, nearly all health plans must cover preventive care recommended by the task force without cost sharing by patients. Implementation of the obesity screening and counseling recommendations remains a work in progress, say experts.

Dr. Caroline Apovian, director of the Nutrition and Weight Management Research Center at Boston University, says many of the patients she treats can’t afford to pay up to $200 a month out of pocket for anti-obesity drugs.

“Coverage has to happen in order for the obesity problem to be taken care of,” says Apovian. “Insurance companies need to realize it’s not a matter of willpower, it’s a disease.”

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