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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. Manufacturing, 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.

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PX1 Research Team

PX1 Research is a primary US cGMP-compliant peptide manufacturer. Our team handles solid-phase synthesis, HPLC purification, lyophilization and in-house analytical testing — every batch ships with a lot-specific Certificate of Analysis.

See how we manufacture

All PX1 Research products are sold strictly for laboratory and research use only. Not for human or veterinary use, diagnosis, treatment or consumption.