FDA approves new version of diabetes drug Mounjaro for weight loss

This image provided by Eli Lilly on Wednesday, Nov. 8, 2023 shows packaging for their new drug Zepbound. (Eli Lilly via AP)

A new version of the popular diabetes treatment Mounjaro can be sold as a weight-loss drug, U.S. regulators announced Wednesday.

The U.S. Food and Drug Administration approved Eli Lilly's drug, named Zepbound. The drug, also known as tirzepatide, helped dieters lose as much as 40 to 60 pounds in testing.

Zepbound is the latest diabetes drug approved for chronic weight management, joining Novo Nordisk's Wegovy, a high-dose version of its diabetes treatment Ozempic. Both are weekly injections.

The FDA approved Lilly's drug for people who are considered obese, with a body mass index of 30 or higher, or those who are overweight with a related health condition, like high blood pressure, high cholesterol or diabetes. The drug should be paired with a reduced-calorie diet and regular exercise, the FDA said.

In the U.S., at least 100 million adults and about 15 million children are considered obese.

The drugs tirzepatide in Zepbound and Mounjaro and semaglutide in Wegovy and Ozempic work by mimicking hormones that kick in after people eat to regulate appetite and the feeling of fullness. Both imitate a hormone called glucagon-like peptide-1, known as GLP-1. Tirzepatide targets a second hormone, called glucose-dependent insulinotropic polypeptide, or GIP.

FDA's approval was based on two large studies: More than 2,500 participants got different strengths of Zepbound and nearly 1,000 people got dummy shots over 16 months. Participants without diabetes who received the highest dose lost about 18 per cent of their weight, or about 41 pounds (19 kilograms), compared to placebo. Those with diabetes, who have a harder time losing weight, cut about 12 per cent, or nearly 27 pounds (12 kilograms), the FDA said.

In another recent study, the drug helped people lose up to a quarter of their weight, or 60 pounds (27 kilograms), when combined with intensive diet and exercise.

Overall, Zepbound appears to spur greater weight loss than Wegovy. Approved for weight loss in 2021, Wegovy helped people lose about 15 per cent of their weight or 34 pounds (15 kilograms), according to study results.

"This would be the most highly efficacious drug ever approved for the treatment of obesity," said Dr. Fatima Cody Stanford, an obesity medicine expert at Massachusetts General Hospital in Boston.

Touted by celebrities and on social media, semaglutide and tirzepatide drugs have already been in such demand that their manufacturers have struggled to keep up. Both have been listed on the FDA's drug shortage site for months. All strengths of tirzepatide are currently listed as available, but a company spokesperson said that could vary by location and demand.

Side effects of the new weight-loss drug include vomiting, nausea, diarrhea, constipation and other gastrointestinal problems. In the most recent published trial, about 10 per cent of people taking tirzepatide dropped out of the study because of such problems, compared to about 2 per cent of people taking dummy shots.

While experts lauded approval of Zepbound, they worried that it wouldn't necessarily mean greater access to the drug, which has been prescribed "off-label" to help people pare pounds.

"Most patients won't be able to afford Zepbound without insurance coverage and many health plans exclude obesity care," said Dr. Katherine Saunders, an obesity expert at New York's Weill Cornell Medicine and co-founder of company focused on obesity treatment.

Eli Lilly and Co. said the list price will be about US$1,000 a month, the same as Mounjaro. The drug is expected to be available in the U.S. by the end of the year, the company said. Dosing strengths are the same for Zepbound and Mounjaro.

Kelly Burns, 50, of St. Petersburg, Florida, lost nearly 100 pounds (45 kilograms) using tirzepatide after joining a study of the drug to treat obesity in 2021. When testing ended and she no longer had access to the medication, she struggled, but eventually lost another 50 pounds (23 kilograms).

"My whole life is completely different," she said. Her health measurements improved and her confidence soared. Now that it is approved for weight loss, Burns plans to ask her insurance company about coverage.

"It would be ridiculous not to," she said, adding: "I want to stay this way as long as I possibly can."