Do Newer Weight Loss Medicines Cause Muscle Loss?

A 2026 review found that newer weight loss medicines cause meaningful muscle loss alongside fat loss during significant weight reduction. Importantly, the proportion of muscle lost was broadly similar to what happens with lifestyle changes alone, without any medicine.

Who Was Studied and How

Researchers pooled results from 20 randomised controlled trials, meaning studies where participants were assigned to treatments by chance rather than by choice. The combined group included 15,782 adults with overweight or obesity. Body composition, specifically lean mass (muscle and other non-fat tissue), was measured using detailed body scanning in each trial.

What the Researchers Found

Between about 1 in 4 and more than 1 in 3 kilograms lost with the weight loss medicines studied came from lean mass rather than fat. Lifestyle interventions without medicine showed a very similar proportion of lean mass loss. Adding resistance training to a lifestyle programme showed the most protective result of any approach studied, with lean mass making up roughly 1 in 6 kilograms of total weight lost.

What This Study Does and Does Not Tell Us

This review draws on a large pool of randomised trials, which adds strength to its findings. Because trial designs and durations varied across the studies included, results may not apply equally to every person or every treatment setting. The review also found that combining resistance training and adequate protein intake with any weight loss approach offered meaningful protection for muscle mass.

About this research: Lean Mass Changes With Incretin Therapy Versus Lifestyle Intervention: A Systematic Review and Meta-Analysis of Randomised Controlled Trials, Diabetes, Obesity and Metabolism, 2026. Read the study summary

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