Experimental drug may help preserve muscle during weight loss injections

A trial drug called Apitegromab may help people losing weight on popular obesity injections keep more muscle mass. The study, published in Nature Medicine, found that participants taking the experimental treatment alongside a weight-loss drug preserved about 1.9 kilograms more lean mass than those on the weight-loss drug alone, while still losing weight.

The research involved 102 adults, most of them women. In the Apitegromab and Mounjaro group, the extra preserved lean mass was about 55% higher than in the comparison group. Researchers also said lean mass accounted for only 14.6% of total weight loss among patients receiving the new drug, a lower share than is often seen with medications such as Wegovy and Mounjaro, where roughly a third of lost weight may come from muscle.

Apitegromab is currently available only in clinical trials and is given by intravenous infusion. It works by blocking a protein involved in muscle breakdown, and it is also being studied for other muscle diseases, including spinal muscular atrophy, or SMA. The company developing it is also considering a self-injection pen version similar to current weight-loss shots.

Experts said the findings are encouraging but preliminary. Dr. Marie Sparckly of the University of Cambridge called them “a promising early piece of evidence,” but not proof of clinical benefit, and said larger, longer studies are needed to determine whether preserving muscle improves strength and quality of life. Dr. Brendan Gabriel of the University of Aberdeen said the treatment may not be needed by everyone, but could help people who lose muscle quickly.

Dr. Raz Hagal, who heads a medical obesity treatment center, stressed that weight-loss drugs themselves do not directly cause muscle loss, but rapid weight reduction can, especially without proper nutrition and exercise. He said obesity treatment must be medically supervised, with a doctor, dietitian or clinical nutritionist, and sometimes a tailored exercise plan focused on strength training and adequate protein intake.