Semaglutide (19.7%), tirzepatide (31.6%), and retatrutide (24.1%) all produced significant weight loss in MC4R KO mice, proving they work independently of the melanocortin obesity pathway.
31.6% weight loss without MC4RTirzepatide achieved the largest weight loss even in mice completely lacking the melanocortin obesity pathway
What the researchers found
Weight loss in MC4R KO mice: semaglutide 19.7%, tirzepatide 31.6%, retatrutide 24.1%. All improved insulin, HOMA-IR, cholesterol, AST/ALT, and suppressed FA synthesis genes. Only tirzepatide reduced RQ. No effect on inflammation genes.
Why it matters
MC4R deficiency causes 5% of severe human obesity. Proving GLP-1 drugs work even without this pathway provides hope for genetically obese patients.
How the study worked
21-day treatment of MC4R KO mice with semaglutide, tirzepatide, or retatrutide, with body composition (Echo-MRI), metabolic parameters, HOMA-IR, liver enzyme/gene expression analysis, and indirect calorimetry.
What this study cannot tell us
Mouse model. 21-day treatment is short. MC4R KO mice don't perfectly replicate human MC4R heterozygous deficiency. All drugs reduced lean mass (a concern).
How to read the evidence
Well-controlled preclinical study with three drug comparisons. Validates MC4R KO mice as a model and GLP-1 drug mechanism independence.
When this study was published
Published in 2025.
The bigger picture
GLP-1 drugs work through mechanisms independent of the melanocortin pathway, suggesting they could be effective first-line therapy even for genetic forms of obesity.
Questions still open
- Would these drugs show similar efficacy in humans with MC4R mutations?
- Does tirzepatide's superior efficacy come from GIP co-agonism in the MC4R-deficient context?
- Should genetic obesity patients be prioritized for GLP-1 therapy?
Common questions
Do GLP-1 drugs work for genetic obesity?
Which drug worked best in genetic obesity mice?
Read the original research
Efficacy of GLP-1 analog peptides, semaglutide, tirzepatide, and retatrutide on MC4R deficient obesity and their comparison.
International journal of obesity (2005)
Citation
Hitaka, Kosuke; Sugawara, Takumi; Matsumoto, Mitsuharu; Nio, Yasunori. (2026). Efficacy of GLP-1 analog peptides, semaglutide, tirzepatide, and retatrutide on MC4R deficient obesity and their comparison.. International journal of obesity (2005). https://doi.org/10.1038/s41366-026-02025-2