Melanotan I vs Retatrutide
A detailed comparison to help you understand the differences and choose the right peptide for your research goals.
Melanotan I
Melanotan I (afamelanotide) is a synthetic analog of alpha-melanocyte-stimulating hormone (α-MSH). It is FDA-approved as Scenesse for erythropoietic protoporphyria (EPP), a rare genetic disorder causing severe sun sensitivity.
Full details →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 →Side-by-Side Comparison
| Aspect | Melanotan I | Retatrutide |
|---|---|---|
| Mechanism | Binds to melanocortin 1 receptors (MC1R) on melanocytes, stimulating eumelanin production. This increases skin pigmentation and provides photoprotection without UV exposure. | 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. |
| Typical Dosage | Clinical: 16mg implant every 2 months. Research protocols for tanning typically use 0.5-1mg daily for loading, then maintenance dosing. | 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. |
| Administration | FDA-approved form is a subcutaneous implant. Research use involves subcutaneous injection. Often combined with minimal UV exposure to enhance results. | Subcutaneous injection, once weekly. Phase 3 trials use pre-filled single-dose pens. Not yet commercially available — estimated FDA approval ~2027-2028. |
| Side Effects | Nausea (especially initially), facial flushing, fatigue, headache, and darkening of existing moles or freckles. | 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. |
| Best For |
Key Differences
Unique to Melanotan I:
Unique to Retatrutide:
Detailed Analysis
Commonalities
Melanotan I and Retatrutide are used for different purposes and have limited overlap in their applications.
Which Should You Choose?
Choose Melanotan I for Skin Health & Aesthetics. Choose Retatrutide for Fat Loss.
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