New Drug May Help Prevent Muscle Loss From GLP-1s

Early clinical trial results show that apitegromab dramatically reduced lean mass loss among people taking tirzepatide, addressing a growing concern tied to rapid weight loss

GLP-1 drugs have disrupted the fitness and wellness industry across the board. Some gym and studio operators have adapted their training approaches to cater to those taking the medication, while others have embraced them wholeheartedly, even offering in-house prescriptions.

But as the medications become more ubiquitous, concerns have arisen about the rapid weight loss that often leads to unwanted loss of muscle mass, which could adversely affect people’s health.

A new drug could target that exact issue, however, according to research published in Nature this week. The clinical trial found that taking the monoclonal antibody apitegromab can help people retain lean body mass while taking tirzepatide (the main ingredient in Mounjaro).

In a group of 102 adults, half were administered apitegromab plus tirzepatide, and the half a placebo with tirzepatide.

The researchers found that despite similar total body weight loss between groups over the 24-week study, those taking apitegromab maintained a 54.9% greater retention of lean mass compared to the placebo cohort. The drug works by blocking myostatin, a protein that can inhibit muscle growth.

Lean muscle loss can comprise 25−40% of total weight loss during GLP-1 therapy, the researchers pointed out. Among the placebo group, lean mass loss took up about 30% of total weight loss — but those taking apitegromab only had 14.6% of total weight loss attributed to lean mass.

Since higher lean body mass — especially skeletal muscle — is associated with a higher metabolism, improved insulin sensitivity and lower risk of Type 2 diabetes, this new drug could be a crucial breakthrough for those taking GLP-1s.

The study authors pointed out that since the trial was relatively short-term, further studies need to be conducted to understand long-term effects and safety. The group was also fairly small and comprised mostly women, presenting limitations for how results could translate into a wider population.

Physical activity is key to maintaining muscle mass while taking GLP-1s. And it’s not just gyms encouraging people on the medications to work out — six leading global fitness bodies came together earlier this year to push for GLP-1s to be integrated into care models that prioritize exercise and nutrition.