PT-141: the MC4R-selective melanocortin agonist
7 min read · Updated September 2026 · MY PEPTIDES Research Team
Key facts
PT-141, also called bremelanotide, is a synthetic cyclic heptapeptide melanocortin-receptor agonist built structurally from Melanotan II. It is made by reworking the C-terminus of the MT-II scaffold, swapping the terminal amide for a free acid (hydroxyl) group, which produces a close cousin with a different receptor-selectivity profile while keeping the lactam-bridged, enzymatically stable architecture of the parent compound. In biochemical and cell-based systems PT-141 works as an agonist at the centrally expressed melanocortin receptors MC3R and MC4R, comparatively more potent at MC4R and substantially weaker at MC1R than Melanotan II. That tilt toward MC4R selectivity makes it a useful tool for isolating MC4R-mediated signaling: G-protein-coupled cAMP and phospholipase-C cascades, intracellular calcium flux, and ERK/MAPK activation inside neuronal and receptor-expressing models. Responses shift with receptor subtype, concentration, exposure time, and model, so PT-141 serves to characterize melanocortin-receptor signaling rather than to predict a defined biological outcome. Bremelanotide is licensed as a prescription medicine in some jurisdictions, but that is a fact about the pharmaceutical product, not about research-grade material, and the two are not interchangeable. What is supplied here is not a licensed medicine, has not been evaluated by the FDA for any use, and is sold strictly for in-vitro laboratory research, with no therapeutic claims attached. For US laboratories it ships pre-mixed with a batch-specific Certificate of Analysis, cold-chain, tracked across the United States next business day, priced in US dollars.
PT-141, which carries the development name bremelanotide, is a synthetic cyclic heptapeptide used in the laboratory as a melanocortin-receptor agonist. It is one of the better-characterized tools in melanocortin pharmacology, and the reason comes down to how it was built. It is a deliberate single-point edit of an existing compound, which turns the two into a tightly controlled pair rather than two unrelated molecules.
For laboratory research only. PT-141 is supplied strictly for in-vitro research. It has not been evaluated by the FDA. This page covers no dosing, administration, or use in humans or animals, and makes no therapeutic claims.
How it relates to Melanotan II, structurally
PT-141 is built from the Melanotan II scaffold. The one change sits at the C-terminus: where Melanotan II is amidated (-NH₂), PT-141 carries a free acid (-OH).
- Melanotan II is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂
- PT-141 is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH
Everything else carries over: the norleucine substitution, the D-phenylalanine, and the lactam bridge that cyclizes the molecule and gives it resistance to enzymatic breakdown. That near-identical structure is exactly the point. A difference in observed response between the two can reasonably be pinned on receptor selectivity rather than on some unrelated structural change, which is why the pair is such a common control in melanocortin work.
Where the receptor selectivity diverges
This is where the pair splits apart. In biochemical and cell-based systems:
- PT-141 is an agonist at MC3R and MC4R, comparatively more potent at MC4R and with substantially reduced activity at MC1R versus Melanotan II.
- Melanotan II is a broad, non-selective agonist across MC1R, MC3R, MC4R, and MC5R, with negligible activity at MC2R.
MC1R is the receptor the literature most closely ties to pigmentation pathways, so a compound that acts far less on MC1R lets investigators study the centrally expressed receptors, MC3R and MC4R, more cleanly. In practice, running PT-141 against Melanotan II is a way to test how much of an observed response actually depends on MC4R rather than on the wider family.
What the research actually examines
PT-141 turns up in the literature mainly as a reference agonist for characterizing melanocortin signaling, and it is worth being precise about what that means. The primary work is in-vitro and preclinical: binding and activation assays and cell-based signaling readouts in defined systems. In that literature PT-141 is a probe for pathways, not a compound with a fixed effect. Reported observations cover:
- MC3R and MC4R binding, activation, and receptor selectivity
- MC4R-mediated cAMP and phospholipase-C signaling, intracellular calcium flux, and ERK/MAPK activation in neuronal and receptor-expressing models
- Comparative pharmacology against non-selective melanocortin analogs
- Structure-activity relationship (SAR) work on cyclic melanocortin peptides
- Receptor-expression and signaling assay development
Reported observations move with receptor subtype, concentration, exposure time, and model system. There is a large body of downstream marketing that ascribes definite outcomes to PT-141; the research-grade material discussed here is used to characterize receptor signaling, and this guide does not extend those in-vitro findings into claims about outcomes.
A note on regulatory status
Bremelanotide holds a marketing authorization in some jurisdictions as a prescription medicine. That is a fact about the licensed pharmaceutical product, not about research-grade material, and the two are not interchangeable. The licensed product is manufactured, tested, and released to pharmaceutical standards for a specific approved use. What is supplied here is not a licensed medicine, has not been evaluated by the FDA, is not manufactured to pharmaceutical standards, and is sold strictly as a laboratory reference compound for in-vitro research. If you need the medicine, that is a prescriber's decision, not a research order.
Supply and format
PT-141 ships as a pre-mixed, ready-to-use solution, so there is no reconstitution step and no lyophilized powder to dissolve, with a batch-specific Certificate of Analysis that records the HPLC-measured purity and the mass-spectrometry identity for that lot. Delivering it as a characterized solution removes the concentration variability that reconstituting a powder can introduce. Refrigerate at 2-8°C on arrival and do not freeze it, since freeze-thaw cycling damages peptides already in solution. See how to store research peptides.
How PT-141 ships in the United States
For US laboratories PT-141 is supplied as a pre-mixed vial with its batch-specific Certificate of Analysis. Every batch is synthesized in our own UK laboratory and then checked again in a US laboratory before it ships, so the material reaching an American bench has been verified on both sides. Orders go out cold-chain from the warehouse that serves the United States, with tracked delivery across the country next business day, priced in US dollars and payable by Visa, Mastercard or Apple Pay. Store refrigerated at 2-8°C on arrival, not frozen.
The broad-spectrum comparator, Melanotan II, ships the same way if you are setting up the selectivity comparison.
What PT-141 is not
- It is not the licensed medicine. Bremelanotide is authorized in some jurisdictions, but this research-grade material is not that product and has not been evaluated by the FDA.
- It is not manufactured to pharmaceutical standards and is not for human or veterinary use.
- It is not a predictor of a defined outcome. It is an MC3R/MC4R-selective reference agonist used to characterize signaling in vitro.
Dosing and administration
We do not publish dosing, reconstitution-for-use, or administration guidance for PT-141. The material is supplied strictly for in-vitro laboratory research and is not for human or veterinary use, so quantity guidance aimed at a person would be inconsistent with what is actually supplied. Experimental concentrations are specific to the receptor, model, and endpoint and belong in the primary literature. The peptide calculator handles concentration arithmetic if you are working from the vial.
Related reading
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Frequently asked questions
- What is PT-141?
- A synthetic cyclic heptapeptide melanocortin-receptor agonist, also called bremelanotide, built structurally from Melanotan II. It serves in laboratory research as an MC3R/MC4R-selective reference agonist, for in-vitro research use only.
- How does PT-141 differ from Melanotan II?
- They share the same cyclic scaffold and differ only at the C-terminus: Melanotan II is amidated, PT-141 carries a free acid. That single edit tilts PT-141 toward MC4R selectivity with substantially reduced MC1R activity, while Melanotan II stays broadly active across MC1R, MC3R, MC4R, and MC5R.
- Which receptors does PT-141 act on?
- MC3R and MC4R, with comparatively higher potency at MC4R. Its MC1R activity is substantially lower than Melanotan II, which is what makes it useful for isolating centrally expressed melanocortin signaling.
- Is PT-141 a licensed medicine or FDA-approved?
- No. Bremelanotide is authorized as a prescription medicine in some jurisdictions, but that applies to the licensed pharmaceutical product, not to research-grade material, and the two are not interchangeable. The PT-141 supplied here is not a licensed medicine, has not been evaluated by the FDA, and is sold strictly for in-vitro laboratory research.
- How is PT-141 supplied and how quickly does it ship in the US?
- It ships as a pre-mixed, ready-to-use solution with a batch-specific Certificate of Analysis, so there is no reconstitution step. Orders are dispatched cold-chain from the warehouse that serves the United States, with tracked delivery across the country next business day, priced in US dollars and payable by Visa, Mastercard or Apple Pay. Refrigerate at 2-8°C on arrival, keep the vial out of the light, and do not freeze it.