Experimental Drug May Help Preserve Muscle During Weight Loss Injections

A new experimental drug, Apitegromab, may help people losing weight with popular obesity shots keep more muscle mass. A study published in Nature Medicine found that participants taking the drug alongside their weight-loss medication preserved more lean mass without reducing weight-loss benefits, but experts say the findings are only an early signal and need further testing.

The study followed 102 adults, most of them women. Those who took Apitegromab with Mounjaro kept, on average, about 1.9 kilograms more lean mass than the group that received Mounjaro alone, a difference of roughly 55%. The researchers also found that muscle accounted for only about 14.6% of the total weight lost among patients taking the new drug.

Apitegromab is currently available only in clinical trials and is given by intravenous infusion. It works by blocking a protein involved in muscle breakdown. The company developing it is also studying it as a treatment for other muscle diseases, including spinal muscular atrophy, and is considering a self-injection pen version similar to existing obesity shots.

The article notes that about a third of weight lost with drugs such as Wegovy and Mounjaro can come from muscle rather than fat. The so-called “Ozempic butt” refers to a thinner or sagging appearance caused by rapid weight loss, and surgeons say complaints about it are increasing. Dr. Mary Sparkley of Cambridge called the results “promising initial evidence,” but said they do not prove long-term clinical benefit. Dr. Brendan Gabriel of Aberdeen said the treatment may help people who are losing muscle quickly. Dr. Raz Hagal said weight-loss drugs themselves do not cause muscle loss, but rapid weight loss, without proper diet and exercise, can. He stressed that obesity treatment must be medically supervised, with a doctor, dietitian or clinical nutritionist, and in some cases strength training and adequate protein intake.