What to Know About Zepbound, the New Weight Loss Drug

The decision by the Food and Drug Administration on Wednesday to approve the weight loss drug tirzepatide adds a potent new tool to the fast-growing arsenal of obesity drugs.

The drug, which will go by the brand name Zepbound, contains the same compound in the sought-after diabetes drug Mounjaro. Many people have used Mounjaro off-label to lose weight since it was initially approved in May 2022, but the move could pave the way for insurance coverage and open the floodgates for more prescriptions.

Zepbound is the second drug in a new class of obesity medications to be approved for weight loss, following Wegovy. And it is now likely the most effective treatment to combat obesity besides bariatric surgery, said Dr. Scott Hagan, an assistant professor of medicine at the University of Washington. But for many, Mounjaro has been hard to find in the year since it hit the market.

“It’s very similar to what we went through with Ozempic,” said Dr. Andrew Kraftson, a clinical associate professor in the division of metabolism, endocrinology and diabetes at Michigan Medicine, noting that demand for weight loss medications has hit a “fever pitch.” Now, he said, patients will likely be clamoring for this new drug. Here’s what to know.

Who qualifies for Zepbound?

The F.D.A. approved Zepbound for people who have a body mass index — a much-criticized metric — of 30 or greater, which technically qualifies them as having obesity, or those with a B.M.I. of 27 who also have certain weight-related conditions, such as high blood pressure. Regulators said the drug should be used in combination with a reduced calorie diet and increased physical activity.

How does tirzepatide work for weight loss?

Zepbound, made by Eli Lilly, is the brand name for tirzepatide when used for weight loss. When the drug is prescribed for diabetes, it is sold under the brand name Mounjaro.

Like semaglutide, the compound in Ozempic and Wegovy, tirzepatide slows down the emptying of the stomach. People feel fuller, quicker and for longer. All three drugs also target the area of the brain that regulates appetite, blunting cravings for many people.

Semaglutide simulates a single hormone in the body, while tirzepatide mimics two, which experts say may be why it’s often more effective at triggering weight loss. In a 72-week clinical trial, funded by Eli Lilly, participants with obesity taking the highest dose of tirzepatide lost around 18 percent of their body weight on average.

If I’m already taking Ozempic or Wegovy, should I switch?

Not everyone reacts to these medications in the same way — someone might lose little to no weight on semaglutide, but shed pounds on tirzepatide, and vice versa, said Dr. Janice Jin Hwang, the division chief of endocrinology and metabolism at the University of North Carolina School of Medicine. People whose weight loss may be most closely tied to other health outcomes — such as those at risk for heart failure or liver disease — may benefit more from losing a significant amount of weight on a drug like Zepbound.

But some people can lose too much weight taking these drugs, Dr. Hwang cautioned. Older people, in particular, should be mindful about their weight loss, since it can lead to shrinking muscle mass. Physicians need to weigh the risks and benefits for each patient, she said.

“There’s no guidelines around any of this,” she said. “We’re just trying to think holistically about the patient.”

Will insurance cover it and what is it likely to cost out of pocket?

Coverage can differ from plan to plan, but some insurance companies will likely cover it for those who meet the F.D.A.’s criteria. Eli Lilly said in a press release that it expects Zepbound will be available in the U.S. by the end of the year at a list price of $1,059.87.

What are the side effects?

In an Eli Lilly-funded study of tirzepatide for obesity, gastrointestinal issues were the most common side effects. Roughly one-third of participants taking the highest dose of tirzepatide experienced nauseaand around one-fifth experienced diarrhea. Some participants also reported abdominal pain, vomiting, constipation, headache and dizziness. The F.D.A. approval states that people taking Zepbound may also experience burping, hair loss and gastroesophageal reflux disease.

Because tirzepatide is so new, we do not know much yet about its long-term effects, Dr. Hwang said. And people taking these kinds of drugs for weight loss typically are advised to stay on them for the rest of their lives, she said.