What to Know About Zepbound (Tirzepatide), the New Mounjaro-Like Weight Loss Drug

The approval by the U.S. Food and Drug Administration (FDA) of the weight loss drug Zepbound (tirzepatide) will give millions of Americans with overweight and obesity a powerful new option for shedding excess pounds.

Zepbound, a once-weekly injected medicine with the same active ingredient as the popular type 2 diabetes drug Mounjaro, was cleared by the FDA for chronic weight management by adults with obesity, and by adults with overweight plus at least one weight-related health issue such as high blood pressure, type 2 diabetes, or elevated cholesterol.

Tirzepatide, the active ingredient in Zepbound and Mounjaro, is the first drug in a new family of medicines that target two hormones — glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) — that are involved in maintaining healthy blood sugar levels and sending signals of satiety from the gut to the brain.

By contrast, the type 2 diabetes drug Ozempic and the weight loss drug Wegovy both contain a different active ingredient, semaglutide, that targets only the hormone GLP-1.

Semaglutide has been available longer, and was considered among the most powerful options for medication-aided weight loss until tirzepatide hit the market, says Fatima Cody Stanford, MD, MPH, an obesity medicine physician, scientist, educator, and policymaker at Massachusetts General Hospital and Harvard Medical School in Boston.

“When semaglutide came out it was the highest weight loss we had ever seen with a drug — that is, until we saw the results for tirzepatide,” Dr. Stanford says.

Clinical trials highlight the dramatic weight loss results for semaglutide, as well as the even more substantial weight loss results for tirzepatide.

A landmark study published in 2021 in the New England Journal of Medicine found that weekly semaglutide shots helped people with overweight and obesity lose an average of 15 percent of their body weight over 68 weeks.

Another pivotal study, published in 2022 in the New England Journal of Medicine, found that tirzepatide helped people with overweight or obesity lose an average of 21 percent of their body weight over 72 weeks when they didn’t make any lifestyle changes.

Just last month, a study published in Nature Medicine found that tirzepatide helped people with obesity lose an average of 27 percent of their body weight over the same time frame when combined with lifestyle changes.

“When we saw the results for tirzepatide it was the first time we crossed that 20 percent threshold for average total body weight loss,” Stanford says. “Right now, if we look at every medicine that has ever come out, this is by far the most potent one that has ever been approved by the FDA.”

Read on for more of Stanford’s insights on Zepbound, including more details on how it works, how it compares with its rival weight loss medication Wegovy, and whether people using it can expect to experience side effects.