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One participant lost 22% of her weight in nine months — substantially faster than the rate seen with approved GLP-1 drugs like Wegovy or Zepbound. Her weight dropped so much that researchers reduced her dose of the treatment, called retatrutide. Still, she continued to feel too nauseous, so she decided by herself to start skipping every other dose.

About a dozen drugmakers are developing new weight-loss treatments aimed at preserving muscle, and industry analysts, clinical trial experts and doctors say they may also need to demonstrate additional health benefits beyond the numbers on a scale to get approved.

Popular weight-loss therapies like Novo Nordisk's Wegovy and Eli Lilly's Zepbound result in both fat and muscle loss.