Where to Buy Melanotan-II in 2026: Sizes, Purity Reports, Verification

Melanotan-II (MT-II) is a synthetic cyclic heptapeptide amide, CAS 121062-08-6, that Pepta Labs lists as a 10 mg lyophilized powder for laboratory research. This guide covers what the compound is chemically, how it is supplied, how to read its purity and identity report, how to store it, and where its regulatory status is documented.

What Is Melanotan-II?

Melanotan-II is a seven-residue peptide. The N-terminal residue is an acetylated norleucine (Ac-Nle) that sits outside a six-residue ring running from aspartate at position 2 to lysine at position 7. The ring is not a disulfide: the molecule contains no cysteine, and closure is a lactam (amide) bond between the beta-carboxyl of Asp2 and the epsilon-amine of Lys7. Position 4 is D-phenylalanine, the only D-amino acid in the sequence, and the C-terminus is a primary amide (-NH2).

Two compounds in the same MSH analogue category are easy to confuse with it on paper. Melanotan-I (INN afamelanotide, CAS 75921-69-6) is a linear 13-residue amide, Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2, with formula C78H111N21O19 and molecular weight 1646.85 Da; it has no ring. PT-141 (INN bremelanotide, CAS 189691-06-3) has the same seven residues and the same lactam ring as Melanotan-II but ends in a free carboxylic acid (-OH) rather than an amide, giving C50H68N14O10 and 1025.17 Da. All three are distinct molecules with distinct CAS numbers.

How Pepta Labs Lists Melanotan-II

Melanotan-II is supplied as a lyophilized (freeze-dried) powder in a sealed glass vial, 10 mg per vial. The purity on the product page is the reversed-phase HPLC (RP-HPLC) result for the production run Pepta Labs sourced, and identity is confirmed by mass spectrometry (MS) on the same run. Pepta Labs does not test in-house: the analytical report comes from an independent laboratory commissioned through a cooperative purchasing group, and it is available by email request before you order. The salt form supplied, acetate or trifluoroacetate, is stated on that report. Our quality page explains how reports are obtained.

How to Verify a Melanotan-II Listing

1. Read the HPLC trace

The RP-HPLC chromatogram shows one main peak with a stated area percentage: 99.3% means 99.3% of the UV-absorbing material eluted as that peak. HPLC purity tells you how much of the peptide fraction is a single species. It does not tell you which species, and it does not report water, counter-ion or residual salt, which is why net peptide content is usually lower than the purity figure. Our HPLC vs mass spectrometry guide explains the distinction.

2. Compare observed mass with theoretical mass

The MS section is what confirms identity. For C50H69N15O9 the monoisotopic mass is 1023.54 Da, so the protonated ion [M+H]+ should appear near m/z 1024.5 and the doubly charged ion [M+2H]2+ near m/z 512.8. An observed [M+H]+ near 1025.5 instead points to the C-terminal acid, PT-141, which is about 1 Da heavier; a value near 1646.8 would be Melanotan-I. A report that quotes only the average molecular weight (1024.18) without an observed m/z has not demonstrated identity. The expected-mass table lists these values for every catalog compound.

3. Know which kind of report you are reading

A production-run report records the HPLC and MS results measured on the run a vendor sourced and is matched to the compound and vial quantity. A lot-specific COA is tied to a lot number printed on the vial. Pepta Labs supplies production-run reports. Ask any vendor which of the two they provide, and be wary of a single document reused across every product in a catalog. The COA verification guide walks through each section of a report.

4. Check the registry number

CAS 121062-08-6 identifies the free Melanotan-II peptide, not its salt, its vial size or its purity grade. A listing that quotes the Melanotan-I CAS (75921-69-6) or the PT-141 CAS (189691-06-3) for a product labelled Melanotan-II is mislabelled. See CAS numbers and molecular weights for the full catalog.

Storage and Shipping

• Shipped at ambient temperature as a sealed lyophilized powder; the dry solid tolerates transit without cold packs.
• On arrival, refrigerate at 2-8 C. For long-term storage keep at -20 C.
• Keep the vial sealed, and protect it from light and moisture.

Our peptide storage guide covers handling in more detail.

US Regulatory Status

Melanotan-II has no International Nonproprietary Name (INN), and Pepta Labs supplies it as a chemical reference material for laboratory research, not as a drug. Its two relatives are different: Melanotan-I carries the INN afamelanotide, which Drugs@FDA lists as the active ingredient of SCENESSE (NDA 210797, approved October 8, 2019), and PT-141 carries the INN bremelanotide, listed as bremelanotide acetate in VYLEESI (NDA 210557, approved June 21, 2019). Those approvals cover the finished prescription products from their sponsors, not research-grade peptide. For the framework governing research peptides in the United States, see peptide legal status 2026.

Frequently Asked Questions

Is Melanotan-II a cyclic peptide?

Yes. The ring is closed by a lactam bond between the Asp2 and Lys7 side chains rather than by a disulfide; the molecule contains no cysteine. The acetylated norleucine sits outside the ring.

How do I tell Melanotan-II from PT-141 on a report?

By the C-terminus and the mass. Melanotan-II (amide) gives [M+H]+ near m/z 1024.5; PT-141 (acid) gives [M+H]+ near m/z 1025.5. The formulas differ by one nitrogen and one oxygen: C50H69N15O9 against C50H68N14O10.

Does the 10 mg on the label refer to free peptide?

Vial quantities in the research market are normally stated as gross lyophilized mass, which includes the counter-ion and any residual water. Check the report for the salt form and, where stated, the net peptide content.

Can I see the analytical report before buying?

Yes. Email support@peptalabs.com and ask for the Melanotan-II 10mg report; no account is required.

Where to Buy Melanotan-II

All products are supplied for laboratory research use only and are not for human or animal use.