What is the difference between Melanotan 1 and Melanotan 2?

They are two distinct synthetic peptides. Melanotan I is a linear α-MSH analogue with a research emphasis on MC1R. Melanotan II is a shorter cyclic melanocortin peptide with a broader melanocortin-receptor research profile (MC1R/MC3R/MC4R/MC5R). They have different CAS numbers, formulas and molecular weights.

Are Melanotan I and II the same peptide?

No. They are chemically distinct compounds with different structures, different chemical identities and different receptor-selectivity research profiles.

Is Melanotan I linear?

Yes. Melanotan I is a linear peptide analogue of α-MSH.

Is Melanotan II cyclic?

Yes. Melanotan II is a cyclic (lactam-bridged) melanocortin peptide.

Is PT-141 the same as Melanotan II?

No. PT-141 (bremelanotide) is a distinct compound that emerged from related melanocortin research, but has its own chemical identity and receptor-selectivity profile.

Are PepDirect Melanotan products intended for human use?

No. PepDirect supplies Melanotan I and Melanotan II strictly as laboratory research materials. Neither is marketed as a medicine, food supplement or product for human or veterinary use.

↳ Research overview

Melanotan I vs Melanotan II

Melanotan I (Melanotan 1) and Melanotan II (Melanotan 2) are two chemically distinct synthetic melanocortin peptides. They share a research heritage as alpha-MSH analogues but have different structures, different receptor-selectivity profiles and separate research literatures.

This guide compares them at the level of chemical identity and receptor pharmacology. It is not a discussion of cosmetic, tanning or physiological use.

For laboratory research context only. PepDirect supplies both compounds as research materials, not for human or veterinary use.

§ At a glance

Melanotan I and Melanotan II at a glance

Both are synthetic peptides derived from alpha-melanocyte-stimulating hormone (α-MSH) research. Their structural design and receptor-selectivity research profiles differ meaningfully.

Structure, Melanotan I: linear α-MSH analogue. Melanotan II: cyclic (lactam-bridged) peptide.
α-MSH relationship, Melanotan I is closely related to NDP-α-MSH / afamelanotide-family research. Melanotan II is a distinct cyclic melanocortin analogue.
Receptor research, Melanotan I: research emphasis on MC1R. Melanotan II: broader melanocortin-receptor research profile (MC1R/MC3R/MC4R/MC5R).
Chemical identity (Melanotan I), CAS 75921-69-6 · C78H111N21O19 · MW ~1646.85 g/mol · PubChem CID 16197727.
Chemical identity (Melanotan II), CAS 121062-08-6 · C50H69N15O9 · MW ~1024.2 g/mol · PubChem CID 92432.
Same compound?, No.

§ Melanotan I

What is Melanotan I?

Melanotan I is a synthetic linear alpha-MSH analogue. In chemical databases the same identifier is also associated with afamelanotide / NDP-α-MSH, the compound investigated in melanocortin-1 receptor research and, in a separately licensed medicinal form under a different regulatory pathway, in dermatological indications.

PepDirect's Melanotan I material is supplied as a laboratory research compound. It is not represented as the licensed medicinal product, and PepDirect does not describe research applications outside laboratory investigation.

§ Melanotan II

What is Melanotan II?

Melanotan II is a synthetic cyclic (lactam-bridged) melanocortin peptide with a distinct chemical identity from Melanotan I. Its research literature includes receptor-selectivity work at melanocortin receptors more broadly, MC1R, MC3R, MC4R and MC5R, rather than emphasising MC1R alone.

§ Structure

How do their structures differ?

Melanotan I is a linear peptide of thirteen residues built directly on the α-MSH backbone. Melanotan II is a shorter cyclic peptide in which a lactam bridge locks the sequence into a constrained ring conformation. That constraint is central to why the two peptides interact differently with the melanocortin receptor family.

§ Receptors

How do their receptor research profiles differ?

Melanotan I research has focused on MC1R pharmacology and on structure-activity work in the linear α-MSH analogue series. Melanotan II research covers a broader melanocortin-receptor scope, including MC3R, MC4R and MC5R in receptor-selectivity studies.

Receptor activity is a mechanistic description. It is not a statement about tanning, sexual function or any human physiological outcome.

§ Interchangeability

Are Melanotan I and II interchangeable?

No. They are structurally distinct (linear vs cyclic), have different chemical identities and are studied in overlapping but non-identical receptor contexts. Research findings for one should not automatically be applied to the other.

§ PT-141

Relationship to PT-141

PT-141 (bremelanotide) arose from further melanocortin-analogue research related to Melanotan II but is a distinct compound with its own chemical identity and receptor-selectivity profile. Melanotan II and PT-141 are not the same peptide and are not interchangeable in research.

§ Research product

View the research products

Melanotan I, Melanotan II and PT-141 are supplied by PepDirect as separate research materials with lot-specific documentation.

View Melanotan II Research Peptide →

§ References

Selected research references

Afamelanotide / Melanotan I · PubChem CID 16197727PubChem (NCBI)
Melanotan II · PubChem CID 92432PubChem (NCBI)
Bremelanotide (PT-141) · PubChem CID 9941379PubChem (NCBI)
NDP-α-MSH structure-activity research (α-MSH analogues)PubMed · Sawyer et al.
Cyclic α-MSH analogues, structure-activity researchPubMed · Hruby et al.
Melanocortin receptor family review (MC1R/MC3R/MC4R)PubMed · Cone

§ FAQ

Frequently asked questions

What is the difference between Melanotan 1 and Melanotan 2?: They are two distinct synthetic peptides. Melanotan I is a linear α-MSH analogue with a research emphasis on MC1R. Melanotan II is a shorter cyclic melanocortin peptide with a broader melanocortin-receptor research profile (MC1R/MC3R/MC4R/MC5R). They have different CAS numbers, formulas and molecular weights.
Are Melanotan I and II the same peptide?: No. They are chemically distinct compounds with different structures, different chemical identities and different receptor-selectivity research profiles.
Is Melanotan I linear?: Yes. Melanotan I is a linear peptide analogue of α-MSH.
Is Melanotan II cyclic?: Yes. Melanotan II is a cyclic (lactam-bridged) melanocortin peptide.
Is PT-141 the same as Melanotan II?: No. PT-141 (bremelanotide) is a distinct compound that emerged from related melanocortin research, but has its own chemical identity and receptor-selectivity profile.
Are PepDirect Melanotan products intended for human use?: No. PepDirect supplies Melanotan I and Melanotan II strictly as laboratory research materials. Neither is marketed as a medicine, food supplement or product for human or veterinary use.

§ Related