Retatrutide results spark questions about how rapid weight loss affects the body

New powerful GLP-1 drugs drop a lot of weight fast. How does that affect health?

New-generation GLP-1 drugs, such as retatrutide, are achieving higher rates of weight loss. How much weight is too much and too fast to lose?

Once people understood glucagonlike peptide 1 (GLP-1) drugs’ potential for weight loss, the race among pharmaceutical companies was on. Among the current options, Wegovy can help people lose an average of 10 percent of their body weight in a year, while people taking Zepbound have had about a 15 percent loss, on average, in the same period. Soon the most powerful GLP-1 treatment to date could hit the market: retatrutide .

Already popular on the online peptide gray market, the new drug, originally developed by Eli Lilly, caused participants in a recent clinical study to lose more than a quarter of their body weight over 80 weeks at the highest dose —results comparable to bariatric surgery. U.S. Food and Drug Administration approval could soon follow.

But bodies don’t just drop weight with no potential adverse effects. Weight loss on its own can change muscle, bone and more. As new-generation GLP-1 drugs promote higher rates of loss , clinicians want to ensure that the desire to shed pounds and see improvements such as better cardiovascular health are balanced with the very real risks that may come with the treatment.

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People typically lose weight when they eat fewer calories than their body expends. A common way to cut calories is to diet, while bariatric surgery removes or changes part of the gastrointestinal tract to reduce food—and therefore calorie—absorption.

GLP-1 is a gut hormone released in response to a meal that helps people feel full . It also increases insulin release and reduces glucose in the blood. Semaglutide (sold as Ozempic and Wegovy by Novo Nordisk) binds to the hormone’s receptor for longer periods of time, making people feel fuller for longer and eat less. Newer versions of GLP-1 drugs, such as tirzepatide (sold as Zepbound and Mounjaro by Eli Lilly) and Novo Nordisk’s upcoming drug CagriSema target more than one type of gut hormone receptor, while retatrutide hits three.