A doctor warns that weight-loss drug semaglutide is shrinking patients' muscle mass at an alarming rate

• Semaglutide has been celebrated as an effective medication for weight loss and appetite reduction. 
• But patients lose muscle mass too, which can undermine the health benefits, says Dr. Peter Attia.
• He recommends trying other weight loss strategies first, and eating enough protein to maintain muscle. 

The popular new weight-loss medication semaglutide is helping people shed weight — but it can also cause a major loss of muscle mass, according to a doctor.

Semaglutide has been described as a "game changer" for treating obesity and was FDA-approved for weight loss in 2021 under the brand name Wegovy. It's also available as Ozempic, which is the same medication, but sold to treat type 2 diabetes (although doctors can and do prescribe it for weight loss as well). 

Semaglutide works by mimicking a natural hormone in the body that helps regulate blood sugar, digestion, and hunger. 

But the FDA, and success stories of semaglutide, doesn't account for patients who are also losing lean muscle, which could worsen their health long-term, Dr. Peter Attia said in a recent clip of his podcast "The Drive."

Attia said body composition, or the ratio of muscle to fat, is a more helpful measure of weight loss results (and subsequent health improvements) than purely the number of pounds lost.  

Attia also noted a trend of people without type 2 diabetes or a high body fat percentage who want to use the medication for small amounts of aesthetic weight loss. 

"Perhaps more disturbing to me is the people who are reaching out to me who are frankly not overweight remotely but are saying 'I really want to lose 10 pounds to look good on my vacation, I should be taking this, right?'" he said. 

Attia said in an earlier post that his patients who have used semaglutide lost weight effectively, but not all of it was body fat. 

"They've lost muscle mass at a rate that alarms me," he said. 

While some muscle mass is expected during weight loss, losing too much can backfire. Muscle mass is important for a healthy metabolism and preventing injury, particularly as we age. 

To offset the possible side effect, Attia said he recommends semaglutide to patients who have already tried other weight loss strategies without medication, and emphasizes that they need to eat enough protein and exercise to preserve muscle. 

There's some promising evidence that a similar medication called tirzapetide may be more effective, Attia said — that drug is still awaiting FDA approval for weight loss.

In the meantime, Attia said it's worth keeping in mind the importance of muscle mass for health, rather than just the number on the scale.  

"Ultimately, it's not your weight that matters, it's your body composition and your health," Attia said.