Melanotan I (Afamelanotide) vs Melanotan II: Mechanism, Specs & Reported Ranges Compared
Side-by-side comparison of Melanotan I (Afamelanotide) and Melanotan II — receptor mechanism, half-life, vial sizes, reconstitution and reported study arms.
By PX1 Research Team · August 4, 2026
Melanotan I (Afamelanotide) vs Melanotan II at a glance
| Melanotan I (Afamelanotide) | Melanotan II | |
|---|---|---|
| Class | linear α-MSH analog | cyclic melanocortin analog |
| Reported half-life | not well characterized | not well characterized |
| Vial sizes | 10 mg | 10 mg |
| Typical reconstitution | 10 mg + 2 mL = 5 mg/mL | 10 mg + 2 mL = 5 mg/mL |
| Research focus | MC1R-selective research | melanocortin receptor research |
Mechanistic difference
Melanotan I is a linear, MC1R-selective α-MSH analog. Melanotan II is cyclic and non-selective, which is why the MC3/MC4 side of its profile appears in the literature.
Reported study ranges side by side
Melanotan I (Afamelanotide)
| Study arm | Reported amount | Cadence |
|---|---|---|
| Loading arm | 500 mcg | daily × 10 days |
| Maintenance | 500 mcg | 2× weekly |
Melanotan II
| Study arm | Reported amount | Cadence |
|---|---|---|
| Loading arm | 250 mcg | daily |
| Maintenance | 500 mcg | 2× weekly |
Practical handling differences
Both arrive lyophilized and shelf-stable. Melanotan I (Afamelanotide) is typically prepared at 10 mg + 2 mL = 5 mg/mL; Melanotan II at 10 mg + 2 mL = 5 mg/mL. Where half-lives differ, the literature's dosing cadence differs accordingly — longer-acting molecules are described weekly, shorter-acting ones daily or split.
Which one appears in which research context
Melanotan I (Afamelanotide) shows up primarily in MC1R-selective research. Melanotan II is used in melanocortin receptor research. They are not interchangeable substitutes; the receptor profile, not the marketing category, determines where each is used.
Documentation and sourcing
Both are supplied at ≥99% HPLC purity with lot-level COAs at /coa. Product pages: Melanotan I (Afamelanotide) · Melanotan II.
How PX1 documents every lot
Every PX1 lot ships with HPLC purity, LC-MS identity, residual solvent, moisture (Karl Fischer), sterility and endotoxin data. Lot documentation is published at /purity-reports, /endotoxin-reports and /coa. Synthesis, purification, lyophilization and vial fill happen in U.S. facilities — see /manufacturing-process.
Research use only. PX1 Research supplies compounds for laboratory and in-vitro research. Nothing here is medical advice, a dosing recommendation, or an offer for human or veterinary use. Figures cited are reported from published laboratory literature.