Trial suggests new treatment may help preserve muscle while using weight-loss injections

A drug designed to promote muscle growth could help tackle one of the biggest concerns surrounding popular weight-loss injections, according to new research.

Scientists have found that a treatment known as apitegromab may significantly reduce the loss of lean body mass in people taking slimming medications such as Mounjaro. The findings offer fresh hope for patients and healthcare professionals who have raised concerns about the amount of muscle that can be lost during rapid weight reduction.

GLP-1 medicines, including Wegovy and Mounjaro, have transformed obesity treatment in recent years. These drugs have helped many people achieve substantial weight loss and improve their overall health. However, experts have repeatedly warned that the weight lost is not made up entirely of fat.

Research has suggested that between 25% and 40% of total weight loss from these medications can come from lean body mass. Lean body mass includes muscles and other non-fat tissues that play an important role in strength, movement and metabolic health.

The latest study indicates there may now be a way to reduce that effect.

Researchers investigated apitegromab, a monoclonal antibody that works by blocking myostatin, a protein that naturally limits muscle growth. By preventing myostatin from doing its job, the drug may help the body preserve more muscle tissue during weight loss.

The study involved 102 participants in the United States. Researchers randomly assigned 51 people to receive apitegromab alongside tirzepatide, the active ingredient found in Mounjaro. The remaining 51 participants received tirzepatide together with a placebo.

After 24 weeks, both groups experienced similar levels of overall weight loss. The difference appeared when researchers examined how much muscle and lean tissue participants had retained.

Those taking apitegromab lost an average of 1.6 kilograms of lean mass. This represented around 14.6% of their total weight loss. By comparison, participants who received the placebo lost an average of 3.5 kilograms of lean mass.

The findings suggest that apitegromab was linked to a 55% greater retention of lean body mass compared with the placebo group.

Researchers believe the results could have important implications because lean body mass contributes significantly to physical strength and long-term health. Muscle tissue burns more calories than fat tissue and is associated with a lower risk of developing conditions such as type 2 diabetes.

The study has attracted attention from obesity specialists.

Professor Alexander Miras, an obesity expert at Ulster University who was not involved in the research, described the findings as highly significant. He noted that while GLP-1 medicines have helped improve people’s ability to perform everyday activities, they have also been associated with reductions in muscle mass and strength.

According to Miras, losing muscle can affect a person’s ability to perform physically demanding tasks, including lifting heavy objects or walking uphill. He suggested the new treatment could potentially lessen those effects and improve physical function further.

Despite the promising results, experts have urged caution.

The trial was funded by Scholar Rock, the company that produces apitegromab. Researchers also acknowledged several limitations, including the relatively small number of participants, the short duration of the study and the fact that most participants were women.

Professor Naveed Sattar, a cardiometabolic medicine specialist at the University of Glasgow, said much larger and longer studies would be needed before firm conclusions could be drawn.

He stressed that while the trial suggests a possible way to reduce muscle loss associated with tirzepatide, it remains unclear whether this translates into meaningful improvements in overall health, movement or physical performance.

For now, experts continue to emphasise the importance of physical activity for people using weight-loss medications. Regular exercise remains one of the most effective ways to preserve muscle mass while losing weight.

As interest in obesity treatments continues to grow worldwide, researchers hope future studies will determine whether muscle-preserving therapies can become an important addition to weight-loss care.