Peter Attia Semaglutide

Doctor Warns About Semaglutide & Muscle Mass

Semaglutide, marketed as Wegovy for weight loss and Ozempic for treating type 2 diabetes, works by mimicking a hormone that regulates blood sugar, digestion, and hunger. This medication has been hailed as a “game changer” for obesity treatment; however, according to Dr. Peter Attia, the medication can lead to a significant loss of muscle mass, which may have long-term health consequences.

“Safe and effective obesity treatments are those which significantly reduce fat mass while minimizing the concurrent loss of lean mass” (Attia, 2023).

There haven’t been many studies which have examined the loss of muscles mass while on semaglutide, but there are at least 2 which may have confirmed Dr Attia’s fears:

In the STEP 1 study, 1961 adults were randomized to receive semaglutide 2.4 mg once-weekly or matched placebo for 68 weeks. Participants who received the drug lost an average of 10.4kg (23.8%) of fat mass and 6.9kg (13.2%) of lean body mass.

A smaller study known as SUSTAIN 8, researchers followed 53 semaglutide users for 52 weeks and found that during their weight loss they had lost 3.4kg (10.2%) of fat mass and 2.3kg (4.5%) of lean body mass.

In both studies the results were the same: While the semaglutide group had significant weight loss, ~40% of the weight lost was from a decline in lean muscle mass.

  • Semaglutide is a weight-loss medication approved by the FDA in 2021 under the brand name Wegovy.
  • The medication can cause a significant loss of muscle mass.
  • Body composition, particularly the muscle-to-fat ratio, is a more valuable measure of weight loss and health improvements.
  • Some patients using semaglutide effectively lost weight but experienced alarming muscle mass loss.
  • Losing excessive muscle mass can have negative consequences for metabolism and injury prevention, especially as individuals age.
  • Health and body composition should be prioritized over solely focusing on the number on the scale.

Although some muscle loss is expected during weight loss, losing too much can have negative consequences, especially as individuals age. The normal loss of lean body mass is usually about 25% of total weight loss, well below the 40% seen in the studies on semaglutide.

According to a spokesperson for Novo Nordisk, the company “did not specifically study the medicine’s impact on muscle mass” in its clinical trials.


Attia, P. (2023). Pros and Cons of GLP-1 weight loss drugs… Podcast.

Attia, P. (2023). Lean mass loss on GLP-1 receptor agonists: a downside of the “miracle drugs”. Blog.

Zhong, P., Zeng, H., Huang, M., Fu, W., & Chen, Z. (2022). Efficacy and safety of once-weekly semaglutide in adults with overweight or obesity: a meta-analysis. Endocrine, 75(3), 718–724.

McCrimmon, R. J., Catarig, A. M., Frias, J. P., Lausvig, N. L., le Roux, C. W., Thielke, D., & Lingvay, I. (2020). Effects of once-weekly semaglutide vs once-daily canagliflozin on body composition in type 2 diabetes: a substudy of the SUSTAIN 8 randomised controlled clinical trial. Diabetologia, 63(3), 473–485.