An experimental drug from the American pharmaceutical company Regeneron, taken together with semaglutide, the active ingredient in the weight-loss pen Wegovy, cut muscle mass loss by 50% in patients with obesity compared with semaglutide alone. The finding comes from a clinical trial with nearly 1,000 participants aged 18 to 65, presented this Thursday (Oct 1) at the European Association for the Study of Diabetes conference in Milan, according to a Reuters report published by Folha de S.Paulo.

The compound, called trevogrumab, is a monoclonal antibody that blocks myostatin, a protein linked to muscle breakdown. In MRI scans of participants' thigh muscles, adding a 75-milligram dose prevented more than 70% of the muscle loss seen with semaglutide alone after 52 weeks, according to a summary of the data released ahead of the presentation.

"We have confirmed that patients on GLP-1 drugs do lose about 30% of their weight as lean muscle mass, something we can prevent with trevogrumab," Regeneron executive Boaz Hirshberg said, according to Reuters. He added that the greatest benefit may be for patients who start treatment with less muscle mass.

What is confirmed and what is still preliminary

The trial also tested a triple combination with a second experimental Regeneron antibody, garetosmab, which targets activin A. According to preliminary 26-week data released earlier, the triple therapy preserved even more lean mass, but raised safety concerns: within the first 26 weeks, two participants receiving higher doses of both antibodies died, Folha reported. One of the deaths had an undetermined cause.

Neither trevogrumab nor garetosmab is available for clinical use. Conference results still need peer review and larger studies before any application for regulatory approval. The race is on, though: at least a dozen companies are developing therapies to preserve muscle during weight loss, and analysts consulted by Reuters project the market could reach US$30 billion in annual sales by 2035.

For people already using GLP-1 pens (the class of injectable drugs behind the recent weight-loss boom), the practical advice remains what doctors recommend today: keep medical follow-up, do regular strength training and eat enough protein, steps that help limit muscle loss while the new combinations are not yet on pharmacy shelves.