Do GLP-1 medications cause muscle loss?

What the trials found

A 2026 systematic review pooled 20 randomised trials with 15,782 participants. It found:^[1]

• Lean mass made up about 25% to 39% of the weight lost with GLP-1-based medicines.
• With diet and lifestyle programmes alone, it was about 26%, a broadly similar share.
• Lifestyle programmes that included strength training lost the smallest share, about 17.5%.

The authors concluded that lean mass loss during large weight loss is substantial whatever the method, and that strength training, enough protein and checking body composition can help preserve muscle.^[1]

Lean mass isn’t the same as muscle

Lean mass means everything that isn’t fat: muscle, but also water, organs and bone. Body scans measure lean mass, so a drop in lean mass doesn’t all come from muscle.

Some researchers argue the worry is often overstated. People usually lose a smaller share of their muscle than of their fat, and physical function tends to improve as weight comes down.^[2] It matters most for older adults and people who had little muscle to begin with.

What helps you keep muscle

• Strength training. In older adults with obesity who cut calories, training three times a week prevented most of the lean mass they would otherwise have lost.^[4] The joint advisory recommends strength training at least three times a week with GLP-1 therapy.^[3]
• Enough protein. Higher targets are proposed while you lose weight, but protein alone is unlikely to be enough without training.^[3] Work out a range with the protein calculator.
• Checking strength over time. Simple tests, such as standing up from a chair or climbing stairs, show whether you’re keeping your strength.^[3]

Talk to your prescriber if

• everyday tasks are getting harder
• you’re losing weight very quickly or feel weak
• you’re 65 or over, or have been told you have low muscle mass

Your prescriber can check your strength and body composition, and look after the medication itself.