Apitegromab Preserves Lean Mass in Tirzepatide Users

A new drug may help preserve muscle mass for people using popular weight-loss medications, according to a recent clinical trial. The study, published in the journal Nature Medicine, found that the monoclonal antibody apitegromab significantly reduced the loss of lean body mass in patients also taking the GLP-1 drug tirzepatide, the active ingredient in Mounjaro.

Weight-loss drugs like tirzepatide and semaglutide (found in Wegovy and Ozempic) have proven highly effective, with studies showing they can help patients lose 10 to 15 percent of their body weight. However, a significant portion of that loss—estimated between 25 and 40 percent—can come from lean body mass, which includes muscle. This reduction is a concern for clinicians, as muscle mass is crucial for physical strength, metabolic health, and the ability to perform daily activities.

The trial involved 102 participants, predominantly women, who were randomly assigned to one of two groups for 24 weeks. Both groups received tirzepatide, but one group also received intravenous infusions of apitegromab, while the other received a placebo. Total weight loss was similar between the groups. However, body composition scans...