Muscle or Fat? The Hidden Risk of Weight-Loss Injections

Weight-loss injections containing the active ingredients tirzepatide and semaglutide, widely used in obesity treatment, are among the most effective weight-loss therapies available today. However, a newly published large-scale observational study has revealed that rapid weight loss may not always mean a healthy body composition.

In the study, which evaluated more than 670,000 users of weight-loss injections, a detailed analysis of approximately 8,000 patients showed that individuals using tirzepatide lost more “lean body mass” (LBM) over 12 months than those using semaglutide.

The study also found that musculoskeletal pain and low exercise tolerance were associated with greater LBM loss. The findings suggest that preserving muscle tissue is critically important, especially in people with limited mobility.

In conclusion, success in obesity treatment should be assessed not only by the weight lost on the scale, but also by how well muscle mass and physical function are preserved.

Source: Murugadoss K, Venkatakrishnan AJ, Soundararajan V. "Greater lean-body-mass decline with tirzepatide than semaglutide in routine care, revealed by body-composition digital phenotyping." medRxiv preprint. DOI: 10.64898/2026.04.11.26350687. Published: April 13, 2026.