PT-141 vs MT-2: How the Two Melanocortin Peptides Compare

PT-141 and MT-2 (melanotan II) are close relatives. PT-141 was developed directly from MT-2, and the two molecules are nearly identical: the same seven residues, the same ring, and a single difference at the very end of the chain. That small change is enough to give them separate identities, separate research histories and very different regulatory status. This guide compares them side by side.

All compounds discussed are sold for laboratory research use only. This page summarizes published research and is not guidance for human or veterinary use.

At a glance

One family, one chemical change

Alpha-melanocyte-stimulating hormone (alpha-MSH) is a 13-residue peptide that proteases break down quickly. Researchers at the University of Arizona set out to make more stable, more potent analogs. Two key steps came out of that work: swapping in norleucine and D-phenylalanine (Sawyer et al., 1980), and then closing the active core into a ring with a lactam bridge (Al-Obeidi et al., 1989). The cyclic result was melanotan II.

PT-141 keeps everything about MT-2 except its last group. MT-2 ends in an amide; PT-141 ends in a free carboxylic acid. In chemistry terms, PT-141 is the deamidated form of MT-2. That single change gives it its own CAS number and a molecular weight one unit higher (Molinoff et al., 2003).

MT-2: the original cyclic analog

MT-2 was designed as a melanotropin, a peptide that stimulates melanin production through the MC1 receptor in skin cells. It is non-selective, meaning it activates several melanocortin receptors rather than one. Early research and human studies focused on pigmentation, and investigators also reported effects linked to central melanocortin receptors (Hadley and Dorr, 2006; King et al., 2007). MT-2 never completed drug development. See the MT-1 vs MT-2 comparison for how it relates to the linear analog.

PT-141: developed for central activity

The central effects seen with MT-2 led Palatin Technologies to develop PT-141 as a compound studied for activity at melanocortin receptors in the brain, especially MC4R in the hypothalamus (Molinoff et al., 2003). Much of its preclinical work is in rodent behavioral models (Pfaus et al., 2004), followed by clinical development (Diamond et al., 2004; Pfaus et al., 2007). Under the name bremelanotide, it became the active ingredient of an FDA-approved product in 2019 for a specific indication (Dhillon and Keam, 2019). The material sold for research is a reagent, not that drug product. See the PT-141 research overview.

Where their research overlaps

• Same receptor family: both are agonists at melanocortin receptors, so both appear in MC4R and MC1R pharmacology research.
• Same structural core: both carry the His-D-Phe-Arg-Trp sequence inside the same lactam ring, the part responsible for receptor binding.
• Shared history: much of the early PT-141 literature cites MT-2 findings as the starting point.

How researchers choose between them

• Pigmentation and MC1R studies: MT-2 is the compound with the deeper literature on melanogenesis.
• Central MC4R and behavioral models: PT-141 was developed and characterized for this purpose, and it has the larger clinical-stage dataset.
• Comparing amide vs acid forms: because the two differ by a single C-terminal group, running both in one system isolates the effect of that change.

What the research does not show

MT-2 was never approved, and most of its human data comes from small early studies. Much of what circulates online about it is anecdotal rather than published. PT-141’s approval covers one specific product and indication; it does not extend to research-grade material. Neither compound’s research supports any use outside a laboratory.

Verify what you’re working with

With only one unit of mass between them, MT-2 and PT-141 are easy to mix up on paper. Identity testing by mass spectrometry, together with the HPLC retention time, is how a lab confirms which one is in the vial. Every Rogue batch is tested by an independent, ISO 17025 accredited U.S. lab, and the QR code on each vial opens that batch’s report on the lab’s own website. See how to read a peptide COA or browse the COA Library.

View PT-141 on Rogue Compounds

View MT-2 on Rogue Compounds

References

1. Sawyer TK, et al. 4-Norleucine, 7-D-phenylalanine-alpha-melanocyte-stimulating hormone: a highly potent alpha-melanotropin with ultralong biological activity. Proc Natl Acad Sci U S A. 1980;77(10):5754-5758. PMID 6777774
2. Al-Obeidi F, et al. Potent and prolonged acting cyclic lactam analogues of alpha-melanotropin: design based on molecular dynamics. J Med Chem. 1989;32(12):2555-2561. PMID 2555512
3. Molinoff PB, et al. PT-141: a melanocortin agonist for the treatment of sexual dysfunction. Ann N Y Acad Sci. 2003;994:96-102. PMID 12851303
4. Hadley ME, Dorr RT. Melanocortin peptide therapeutics: historical milestones, clinical studies and commercialization. Peptides. 2006;27(4):921-930. PMID 16412534
5. King SH, et al. Melanocortin receptors, melanotropic peptides and penile erection. Curr Top Med Chem. 2007;7(11):1098-1106. PMID 17584130
6. Pfaus JG, et al. Selective facilitation of sexual solicitation in the female rat by a melanocortin receptor agonist. Proc Natl Acad Sci USA. 2004;101(27):10201-10204. PMID 15226502
7. Diamond LE, et al. Double-blind, placebo-controlled evaluation of the safety, pharmacokinetic properties and pharmacodynamic effects of intranasal PT-141, a melanocortin receptor agonist, in healthy males and patients with mild-to-moderate erectile dysfunction. Int J Impot Res. 2004;16(1):51-59. PMID 14963471
8. Pfaus J, Giuliano F, Gelez H. Bremelanotide: an overview of preclinical CNS effects on female sexual function. J Sex Med. 2007;4 Suppl 4. PMID 17958619
9. Dhillon S, Keam SJ. Bremelanotide: first approval. Drugs. 2019;79(14):1599-1606. PMID 31429064