How weight loss drugs may trigger severe muscle loss

Weight loss drugs have transformed how millions approach obesity treatment. However, experts are now warning users about the dangers of rapid weight loss. Drugs such as Mounjaro and Wegovy can lead to a rapid loss of lean muscle equivalent to nearly a decade of ageing.

Weight loss drugs and muscle loss

In 2024, more than one billion people worldwide had obesity, according to the UN. Weight loss drugs such as Wegovy and Mounjaro offer huge potential to tackle soaring obesity globally, but they may come at a hidden cost if the approach isn’t right. These weight loss treatments may lead to significant lean muscle loss, along with fat. This can lead to reduced strength, especially in older people, who are at increased risk of frailty and falls.


A 2024 study by researchers at the Pennington Biomedical Research Center found that weight loss drugs, including GLP-1 receptor agonists, may lead to muscle loss. The study, titled “Muscle Matters: The Effects of Medically Induced Weight Loss on Skeletal Muscle”, published in The Lancet, showed that people can lose 25% to 39% of their total weight as muscle over 36 to 72 weeks on these medications. This rate of muscle loss is significantly higher than what is seen in weight loss achieved through non-pharmacological caloric restriction or normal ageing.

This decline in muscle mass can lead to decreased immunity, an increased risk of infections, poor glucose regulation, and other health risks.

“We have to be mindful of the side effects that we are seeing with the new weight loss medications, such as a person eating less while on the medications and not getting the appropriate amount of dietary vitamins and minerals. Also, when a person loses weight, they are not only losing fat, they also lose muscle. We are looking at how that muscle loss can be better managed with the consumption of an adequate amount of protein along with an optimum amount of exercise,” Dr Heymsfield, professor of metabolism and body composition, said.

How resistance training may help

An evidence review published in the journal Diabetes last year found that use of these drugs caused “rapid and significant loss of lean mass”, with an average of 6 kg per person. The study also emphasised the importance of resistance training.

As the use of the anti-diabetic and weight loss drug Ozempic skyrockets, concerns about the medication’s side effects are also rising. A recent study published in the journal Cell Metabolism by researchers at Massachusetts General Hospital and Harvard Medical School found that while women and older adults are at increased risk of muscle loss, higher protein intake may help prevent it.

Lead researcher Melanie Haines, M.D., of Massachusetts General Hospital, found that approximately 40% of the weight lost from taking semaglutide comes from lean mass, including muscle. It is not yet known who is at the highest risk for muscle loss or how it affects blood sugar levels, Haines added.

“Older adults and women may be more likely to lose muscle on semaglutide, but eating more protein may help protect against this,” Haines said. “Losing too much muscle may reduce the benefits of semaglutide on blood sugar control. This means preserving muscle during weight loss with semaglutide may be important to reduce insulin resistance and prevent frailty in people with obesity.”

The NHS also points out that weight loss drugs should not be considered as standalone treatments; instead, they should be paired with the right diet and exercise.

Dr Matthew Wade, a researcher at ukactive, a fitness non-profit that represents UK gyms, told The Times that resistance training and lifting weights may help to prevent muscle loss. “The rapid rollout of GLP-1 has shown dramatic results for patients, but in order to avoid weakening the body, there are simple and effective strength exercises that are essential for sustainable results,” Wade said.

“The health and fitness sector can support people taking weight loss medications, but we want to see the Government go further by working with the fitness, nutrition, and pharmaceutical industries to deliver the critical wraparound support patients need,” he added.

Note: The information provided in this article is for educational purposes only and is not intended as medical advice. Always consult a qualified healthcare professional before starting any new medication or treatment, or before changing your diet or supplement regimen.

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