A new review has raised questions about the nature of weight lost through injections such as Mounjaro and Wegovy, suggesting that a substantial share may come from muscle rather than fat.
Mounjaro has a major impact on facial muscles
Across 36 studies, researchers found that lean mass accounted for a significant proportion of total weight loss. Specialists say this may help explain reports of facial changes, often described as "Ozempic face", where users appear gaunt, with hollow cheeks and more pronounced bone structure.
Dr Ruby Aktar, a neuroscientist and weight-loss expert at Queen Mary University of London, said: "The aesthetic change often referred to as ‘Ozempic face’ is typically linked to the pace and composition of weight loss, rather than the medication itself.
"When weight is lost quickly, the body doesn’t just draw from fat stores, it can also break down lean muscle and the structural fat that supports areas like the face."
The findings, set to be presented at the American College of Physicians' Internal Medicine Meeting in San Francisco, have sparked fresh concern among doctors.
They warn that muscle loss doesn’t just affect appearance – it can have serious health consequences, including frailty and an increased risk of falls.
Dr Charlotte Suetta, a geriatric consultant at Copenhagen University Hospital, said: "Treatment should be paired with strategies likely to preserve muscle health, especially resistance exercise and adequate protein intake."
Rapid weight loss can leave skin stretched and unsupported, particularly in the face, where muscle plays a key role in maintaining structure and tone. The faster the weight drops, the more dramatic the effect can be.
There are also concerns about what happens when patients stop taking the drugs. Previous research suggests many regain weight quickly, potentially undoing benefits while compounding health risks.
For older adults, the stakes may be even higher.
Dr Suetta added: "In older adults, preservation of muscle may be decisive for whether weight loss leads to better health or greater vulnerability.
"For older adults especially, this is not just about body composition. It is about mobility, falls, frailty, and the ability to maintain an independent life."