Retatrutide vs Substance P
A detailed comparison to help you understand the differences and choose the right peptide for your research goals.
Retatrutide
Retatrutide (LY3437943) is a first-in-class triple agonist peptide targeting GIP, GLP-1, and glucagon receptors simultaneously. Developed by Eli Lilly, it is currently in Phase 3 clinical trials and has demonstrated the highest weight loss of any obesity medication to date — up to 28.7% body weight reduction at 48 weeks. The triple-receptor mechanism represents the next evolution beyond dual agonists like tirzepatide.
Full details →Substance P
Substance P is an 11-amino acid neuropeptide involved in pain transmission, inflammation, and various neurological processes. While not used therapeutically itself, understanding it is crucial for pain research.
Full details →Side-by-Side Comparison
| Aspect | Retatrutide | Substance P |
|---|---|---|
| Mechanism | Retatrutide is a synthetic peptide that activates three incretin/metabolic hormone receptors: (1) GLP-1 receptor — appetite suppression, insulin secretion, delayed gastric emptying, (2) GIP receptor — enhanced insulin sensitivity, improved fat metabolism, (3) Glucagon receptor — increased energy expenditure, hepatic fat mobilization, thermogenesis. The glucagon receptor component is the key differentiator, adding an energy-expenditure mechanism absent from GLP-1 and dual GIP/GLP-1 agonists. The molecule uses a C20 fatty diacid for albumin binding, enabling once-weekly dosing. | Binds primarily to NK1 receptors to transmit pain signals from peripheral nerves to the CNS. Also promotes inflammation, causes vasodilation, and stimulates immune cells. |
| Typical Dosage | Phase 2 trial doses: 0.5 mg, 4 mg, 8 mg, and 12 mg weekly. The 12 mg dose produced maximum weight loss (28.7%). Phase 3 trials are evaluating doses up to 12 mg. Dose escalation schedule similar to other GLP-1s (start low, increase every 4 weeks). Final approved dosing not yet established — Phase 3 trials ongoing. | Not used as a therapeutic agent. NK1 receptor antagonists (blocking Substance P) are used clinically for chemotherapy-induced nausea. |
| Administration | Subcutaneous injection, once weekly. Phase 3 trials use pre-filled single-dose pens. Not yet commercially available — estimated FDA approval ~2027-2028. | Research compound only. Therapeutic applications focus on blocking rather than administering Substance P. |
| Side Effects | Phase 2 data: nausea (up to 25%), diarrhea (up to 22%), vomiting (up to 15%), constipation, decreased appetite. GI side effects were dose-dependent and generally mild-to-moderate. Lower rates of nausea compared to semaglutide, potentially due to GIP component. Increased heart rate observed at higher doses. | Administration would cause pain, inflammation, and neurogenic responses. Not given therapeutically. |
| Best For |
Key Differences
Unique to Retatrutide:
Unique to Substance P:
Detailed Analysis
Commonalities
Retatrutide and Substance P are used for different purposes and have limited overlap in their applications.
Which Should You Choose?
Choose Retatrutide for Fat Loss. Choose Substance P for Cognitive Performance.
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