Apitegromab Added to Tirzepatide Helps Retain Lean Body Mass in US Obesity Trial

A US trial published in Nature Medicine found that adding apitegromab to tirzepatide helped retain lean body mass during obesity treatment, even as total weight loss was similar between groups.

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The Guardian reported that researchers randomly divided 102 participants into two groups, with 51 given apitegromab alongside tirzepatide and 51 given a placebo with tirzepatide.

BBC

After 24 weeks, the Guardian said participants given apitegromab lost on average 1.6kg (3.5lb) of lean mass, while those given tirzepatide alongside a placebo lost on average 3.5kg of lean mass.

The same report said the apitegromab group showed a 55% greater retention of lean mass relative to placebo, with most side effects deemed mild and similar between groups.

Prof Alexander Miras of Ulster University, who was not involved in the work, said: "This means that [people] may be less able to lift heavy weights, for example, or walk up a hill," linking GLP-1s to muscle loss and strength concerns.

The BBC framed the research as a potential way to reduce muscle decline linked to "Ozempic butt," saying the US research suggests around a third of the weight loss from GLP-1 obesity jabs like Wegovy and Mounjaro can come from muscle rather than fat.

In the trial with 102 adults, mostly women, the BBC said those who took apitegromab with their obesity medication maintained more muscle while still losing fat, based on body scans.

The Guardian

The BBC reported that people who also received apitegromab kept around 1.9kg or 55% more muscle, or 'lean mass', and that lean mass made up 14.6% of total weight loss in the apitegromab group compared with 30.2% in the placebo group.

Dr Marie Spreckley of Cambridge University, who was not involved in the research, cautioned that the findings were promising but should be viewed as "encouraging early evidence" rather than definitive proof of clinical benefit.

The BBC also said apitegromab is currently only available for use in clinical trials and must be given into a vein as an infusion, with the company investigating whether people could self-inject using a special injection pen.

The Guardian said the study’s limitations included that most participants were women and that the study was small and short in duration, while also noting that the number of people experiencing side effects were similar between groups.

“A drug that promotes muscle growth could significantly reduce the loss of lean body mass when using slimming jabs, research suggests”

The Guardian

Prof Naveed Sattar of the University of Glasgow told the Guardian that far larger-scale and longer trials were needed, not least to check safety, after describing the work as an early-stage trial.

Sattar said: "it’s too early to say whether this actually benefits peoples health or ability to move or function better," and he added that people prescribed these drugs should be supported to increase their physical activity.

The BBC similarly said experts want more evaluation studies before recommending apitegromab, and it described the need to check whether preserving muscle improves strength, wellbeing and long-term health outcomes.

Together, the two reports positioned apitegromab as a monoclonal antibody that blocks a protein involved in muscle breakdown, with the next step being larger, longer studies to determine whether the retained lean mass translates into better function and health.