PT-141 (Bremelanotide) and Melanotan II (MT-II) are structurally related synthetic peptides that activate the melanocortin receptor family. They share a common backbone but differ at the C-terminus — and that small structural change produces meaningfully different research profiles. This article compares them across receptor selectivity, research applications, and observable effects.
Shared structure
Both peptides are based on the α-MSH (alpha-melanocyte stimulating hormone) heptapeptide core with modifications for stability:
- PT-141: Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-OH
- Melanotan II: Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-NH₂
The difference is a single C-terminal modification: PT-141 has a free carboxylic acid (-OH); Melanotan II has an amide (-NH₂).
How the C-terminal change shifts selectivity
The C-terminal amide on Melanotan II appears to favour MC1R binding (driving melanogenesis/pigmentation), while the free acid on PT-141 reduces MC1R affinity and shifts the activity profile toward central MC4R pathways. The structural change is small but the receptor-binding consequence is significant.
Side-by-side receptor profile
| Receptor | MT-II potency | PT-141 potency |
|---|---|---|
| MC1R (melanogenesis) | High | Low |
| MC3R (energy, inflammation) | High | Moderate |
| MC4R (appetite, sexual) | High | High (selective focus) |
| MC5R (exocrine, sebum) | High | Moderate |
Observable effects in research
| Effect | MT-II | PT-141 |
|---|---|---|
| Skin pigmentation | Pronounced | Minimal |
| Appetite suppression | Strong | Mild |
| Sexual response activation | Strong | Strong |
| Spontaneous erection (research models) | Yes | Yes |
| Nausea | Common at higher doses | Common (~40% in trials) |
| Blood pressure elevation | Mild | Mild to moderate |
Research applications — MT-II
- Melanogenesis pathway research (UV-independent pigmentation)
- Pan-MC receptor pharmacology studies
- Appetite regulation models
- Photoprotection research (the original development angle)
Research applications — PT-141
- Selective MC4R pharmacology
- CNS sexual response circuit studies
- Hypoactive sexual desire disorder clinical research
- Autonomic regulation through central MC4R
Clinical translation
PT-141 reached regulatory approval in 2019 (Vyleesi for premenopausal HSDD in women). Melanotan II has remained a research-only peptide — the non-selective profile meant clinical applications became fragmented, and the pigmentation effect (originally the development target) was overshadowed by safety concerns related to atypical mole development in some research subjects.
Why selectivity matters in this family
The melanocortin receptors have wide tissue distribution. Activating all of them simultaneously produces a complex effect profile that is hard to control in clinical settings. Selective MC4R targeting (PT-141) isolates one specific pathway, making side-effect prediction more tractable. The shift in this peptide family is toward more selective compounds.
Stability and reconstitution
Both peptides are supplied lyophilised and reconstitute in bacteriostatic water at 1–2 mg/mL. The cyclic backbone of both confers good stability. Refrigerated reconstituted material retains potency for approximately 4 weeks. Protect from light to prevent tryptophan photodegradation.
Pharmacokinetic comparison
| Attribute | MT-II | PT-141 |
|---|---|---|
| Subcutaneous bioavailability | ~80% | ~80% |
| Plasma half-life | ~2 hours | ~2 hours |
| Onset | ~30 min | ~45 min |
| Duration | ~4-6 hours | ~4-6 hours |
Chempeptides supplies both peptides with batch-specific CoA — see the catalogue, our MT-II article, and our PT-141 article for compound-specific detail.
Research use only.