A drug may help people on GLP-1 meds preserve muscle

When people drop weight on GLP-1 meds, they can also lose muscle. But a proof-of-concept drug might help preserve this lean tissue.

When taken at the same time as a powerful weight loss medication, the experimental antibody let patients hang on to lean body mass, scientists report June 8 in Nature Medicine.

The drug has not yet been approved by the U.S. Food and Drug Administration and is available only via intravenous infusions, so it’s not something consumers are likely to get their hands on any time soon, says study coauthor Richard Pratley, a clinician and metabolic disease researcher at the AdventHealth Translational Research Institute in Orlando, Fla. But the work cracks open the door on how to save muscle that might otherwise be lost.­ That may be good news for GLP-1 users, but important questions remain.

Scientists don’t know if retaining lean mass like this actually translates to better health. They also don’t know the long-term effects or whether such drugs might help people beyond GLP-1 users, like older individuals whose muscles are shrinking with age. “We need to learn what these medications are capable of,” Pratley says.

GLP-1 drugs can spark drastic and rapid weight loss. But not all the weight lost is fat. Some 25 to 40 percent is lean body mass, which includes a person’s muscle, organs and blood. Though patients may lose some muscle when they drop lean mass, it may be less than people think, says Randy Seeley, an obesity researcher at University of Michigan Medical School in Ann Arbor who was not involved with the study. Despite what you hear from social media influencers about the importance of maintaining muscle mass when taking Ozempic, he says, for most people, “this isn’t a problem that needs to be solved.”

That view is supported by clinical trials on GLP-1 drugs. For most participants, Pratley says, losing lean body mass doesn’t seem to impact function. “If anything, people tend to become more functional,” he says, “because they can do more stuff and it’s easier to move around.”

But it’s not clear how previous clinical trial data translate to the wider population of people using weight loss medications in real life. There may be people for whom a lean mass–preserving drug could be useful. In the new study, the researchers tested an antibody that shuts down myostatin, a protein that puts the brakes on muscle growth. Removing these brakes should counteract some of the lean mass loss that accompanies weight loss, the researchers hypothesized.

The drug, apitegromab, has already been tested for another condition, spinal muscular atrophy. For the new study, Pratley’s team tested it in a clinical trial of 102 people with body mass indexes classified as overweight or obese. All participants got weekly injections of the weight loss drug tirzepatide for 24 weeks; half also received a monthly infusion of the antibody drug. People in both groups lost about the same amount of weight, but those who received the antibody lost half as much lean mass as those who took only tirzepatide.

The researchers “absolutely show that they can preserve lean mass,” Seeley says. But for him, the outstanding question is whether that preservation is meaningful. There are hints it might be. Participants in the antibody group had slightly greater grip strength than their counterparts and scored a bit better on a test measuring leg strength and endurance.

That’s a step in the right direction, Pratley says. But the gains were minor and the number of study participants was small. It’s something scientists could explore in future studies­ along with how apitegromab and related drugs work in older, frailer people.

The goal is to fine-tune patients’ medications to their specific needs, Pratley says, finding “the right drug for the right patient at the right time.”

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