Muscle growth drug may reduce lean tissue loss with slimming jabs, study finds
7 reported2 unconfirmed
A small trial has found that a muscle growth drug called apitegromab may help reduce the loss of lean body mass in people using the slimming jab tirzepatide, the drug in Mounjaro. Researchers in the US randomly divided 102 participants into two groups, with 51 given apitegromab alongside tirzepatide and 51 given a placebo with tirzepatide. After 24 weeks, total weight loss was similar for both groups, but those on apitegromab lost on average 1.6kg of lean mass, compared to 3.5kg in the placebo group. The study, funded by apitegromab producer Scholar Rock, was published in the journal Nature Medicine. Experts not involved in the work called the findings important but cautioned that larger and longer trials are needed to check safety and health benefits.
What’s reported
GLP-1 based jabs such as Wegovy and Mounjaro are effective for weight loss but studies suggest 25-40% of total weight loss is lean body mass, including muscle.
Apitegromab is a monoclonal antibody that blocks myostatin, a protein involved in inhibiting muscle growth.
The trial involved 102 participants randomly divided into two groups of 51.
After 24 weeks, the apitegromab group lost on average 1.6kg of lean mass (14.6% of total weight loss), while the placebo group lost 3.5kg.
Use of apitegromab was associated with a 55% greater retention of lean mass relative to placebo.
Side-effects were similar between groups, with most deemed mild.
Most participants were women, and the study was small and short in duration.
Open questions
Whether the retention of lean mass translates into improved health or physical function.
The long-term safety and efficacy of apitegromab in combination with tirzepatide.
Key figures
Prof Alexander Miras, obesity expert at Ulster University (not involved in the work)
Prof Naveed Sattar, cardiometabolic medicine expert at the University of Glasgow (not involved in the work)
Researchers in the US (not named individually in the article)
Scholar Rock (apitegromab producer, funded the trial)
Sources: The Guardian
