When it comes to coverage for the pricey GLP-1 weight-loss drugs Wegovy and Zepbound, only a fifth of large U.S. companies cover the medications in their health insurance plans, a new survey shows.

In a report published Wednesday in the journal Health Affairs, researchers also found that a third of companies that do cover the medications say coverage has a “significant impact” on their plans' prescription drug spending.

Obesity can fuel poor health and affects a significant chunk of the U.S. population, and these medications can help, the survey authors wrote. However, concerns linger about the drugs' high costs and the likelihood that they need to be used indefinitely.

“Employers are really trying to thread the needle right now,” study author Matthew Rae, associate director for the program on the health care marketplace at KFF, told NBC News. “They’re trying to figure out what is the right balance between the advantages to employees, potential health benefits and the cost of these drugs. And at this point, all of those things aren’t sorted out.”

Dr. Susan Spratt, an endocrinologist and senior medical director for the Population Health Management Office at Duke Health in North Carolina, told NBC News the results were “disheartening.”

“People who are rich can afford to pay the $1,000 per month for this medication,” she said. “We are just widening health disparities by making it harder for patients to access life-changing medication.”

About 154 million people get health insurance through their jobs, according to KFF. The survey, taken from January through July, included responses from more than 2,100 employers that have at least 200 workers and offer health benefits.

Half of the employers said they don’t cover the drugs, while nearly a third said they don’t know if they cover them; fewer than 1 in 5 said they provide such coverage.

America’s largest firms — 5,000 or more workers — didn't do much better: Just over a quarter said they cover the drugs, while almost two-thirds say they don’t.

About 40% of adults in the U.S. have obesity, according to the U.S. Centers for Disease Control and Prevention. While obesity rates have plateaued over the past decade, rates of severe obesity have increased, from 7.7% to 9.7%. 

Dr. Christopher McGowan, a gastroenterologist who runs a weight-loss clinic in North Carolina, said there is a tendency to blame employers and insurance companies for the lack of coverage, but that blame is “misdirected.” 

“The root of the problem is cost. Plain and simple,” McGowan told NBC News. “It’s economically impossible to provide coverage for everyone in need without drastically hiking rates or putting health plans at risk of bankruptcy.”

Novo Nordisk and Eli Lilly did not respond to requests for comment from NBC News.

The survey also found that about half of employers that cover the weight loss drugs have certain requirements associated with their coverage, which Rae said would limit access for some employees but save money. The requirements can include meeting with a dietitian or participating in a lifestyle or weight-loss program either before or while taking the drugs.

Among large firms that don’t currently cover GLP-1 drugs for weight loss, only about 3% said they’re “very likely” to do so in the next year.

Despite the current lack of coverage, the survey found that nearly half of large firms said it will be “very important” or “important” to cover GLP-1 drugs in the future, for their employees’ satisfaction.