All Three GLP-1 Drugs Work in MC4R Knockout Mice — Even Without the Melanocortin Pathway
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.
Quick Facts
What This Study 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.
Key Numbers
How They Did This
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.
Why This Research Matters
MC4R deficiency causes 5% of severe human obesity. Proving GLP-1 drugs work even without this pathway provides hope for genetically obese patients.
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.
What This Study Doesn't 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).
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- 31.6% weight loss without MC4R Tirzepatide achieved the largest weight loss even in mice completely lacking the melanocortin obesity pathway
- Evidence Grade:
- Well-controlled preclinical study with three drug comparisons. Validates MC4R KO mice as a model and GLP-1 drug mechanism independence.
- Study Age:
- Published in 2025.
- Original Title:
- Efficacy of GLP-1 analog peptides, semaglutide, tirzepatide, and retatrutide on MC4R deficient obesity and their comparison.
- Published In:
- International journal of obesity (2005) (2026)
- Authors:
- Hitaka, Kosuke(2), Sugawara, Takumi(2), Matsumoto, Mitsuharu(2), Nio, Yasunori
- Database ID:
- RPEP-15297
Evidence Hierarchy
Frequently Asked Questions
Do GLP-1 drugs work for genetic obesity?
Yes. This study proved semaglutide, tirzepatide, and retatrutide all cause significant weight loss even in mice that completely lack the MC4R melanocortin pathway — the most common cause of genetic obesity.
Which drug worked best in genetic obesity mice?
Tirzepatide (31.6% weight loss) outperformed retatrutide (24.1%) and semaglutide (19.7%), suggesting the GIP receptor co-activation provides extra benefit when the melanocortin pathway is absent.
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Cite This Study
https://rethinkpeptides.com/research/RPEP-15297APA
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
MLA
Hitaka, Kosuke, et al. "Efficacy of GLP-1 analog peptides, semaglutide, tirzepatide, and retatrutide on MC4R deficient obesity and their comparison.." International journal of obesity (2005), 2026. https://doi.org/10.1038/s41366-026-02025-2
RethinkPeptides
RethinkPeptides Research Database. "Efficacy of GLP-1 analog peptides, semaglutide, tirzepatide,..." RPEP-15297. Retrieved from https://rethinkpeptides.com/research/hitaka-2026-efficacy-of-glp1-analog
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkPeptides research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.