Ozempic, a drug originally developed for diabetes but now widely used for weight loss, has been praised for helping many people shed extra pounds.
However, questions have been raised about whether the drug also causes a loss of ‘lean mass,’ which includes muscles and other non-fat tissues in the body.
Losing too much muscle mass could lead to weakness and mobility problems, especially in older adults.
A new study in mice, published in the journal Cell Metabolism, suggests that while muscle mass changes less than some had feared, muscle strength may still decrease in certain cases.
The research was led by Katsu Funai, PhD, an associate professor at the University of Utah College of Health. He says that before we can help people avoid losing muscle, we need to confirm whether muscle loss is truly happening in patients taking the drug.
In the study, mice given Ozempic lost about 10% of their lean mass. Surprisingly, most of this loss was not from skeletal muscles but from other tissues such as the liver, which shrank by nearly half.
Researchers note that organ size changes can happen naturally with weight gain and loss, and shrinking organs like the liver doesn’t necessarily mean they function less effectively. This suggests that the lean mass loss seen here might not be harmful by itself.
When looking specifically at skeletal muscles, the researchers found some did shrink—on average, by around 6%—while others stayed the same size. Some of this reduction could simply be the body returning to its baseline.
When someone gains weight, they often gain some muscle as well, because the body has to work harder to move. Losing fat can then reduce that extra muscle without affecting overall quality of life.
But size isn’t the whole story. The team measured how much force the muscles could generate and found that for certain muscles, strength went down even if their size didn’t change much. For other muscles, strength was unaffected.
This raises new concerns because muscle weakness can impact daily function, especially in people over 60 who are already at higher risk of losing muscle and mobility. Funai points out that physical function is a strong predictor of both quality of life and longevity.
The researchers caution that their results in mice may not directly apply to humans. Mice and people gain and lose weight differently.
For example, obesity in humans is often linked to reduced physical activity, while mice generally stay active regardless of their weight. In this study, the mice became overweight by eating a high-fat diet, but human obesity has many causes, including genetics, lifestyle, and aging.
Rather than assuming these results are the same in people, the team says their work highlights the urgent need for human clinical studies.
They stress that trials should not only measure changes in muscle size but also test for changes in muscle strength. This should apply not just to Ozempic but also to other weight-loss drugs that will be introduced in the coming years.
This study gives a more nuanced picture of Ozempic’s possible effects on the body. It suggests that while significant muscle loss might not occur, muscle strength could still be affected in ways that matter for health and daily living. For older adults, this could mean an increased risk of frailty or reduced mobility.
Because the research was done in mice, we cannot yet know if the same effects occur in people. Until human trials are completed, patients and doctors should keep these questions in mind and consider ways to preserve muscle strength during weight loss—such as strength training and adequate protein intake.
If you care about obesity, please read studies about Scientists find two big contributors to obesity and findings of Higher dose of this diabetes med could improve blood sugar and weight loss.
For more information about obesity, please read studies about Scientists find new key cause of obesity and findings of Double whammy: diabetes drug also knocks out obesity.
The study is published in Cell Metabolism.
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