PT-141 (Bremelanotide): A Research Peptide Overview

PT-141 (bremelanotide) is a synthetic cyclic heptapeptide analogue of α-melanocyte-stimulating hormone (α-MSH), with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. The ring is closed by a lactam bridge between the Asp and Lys side chains, and the molecule is a known active metabolite of the earlier analogue Melanotan II. As the acetate salt it carries CAS number 1607799-13-2, the molecular formula C52H72N14O12, and a molecular weight of 1085.22 g/mol.

As a research reference material it is supplied as a lyophilized powder and characterised by HPLC for purity and mass spectrometry for identity.

In the laboratory, PT-141 is used in binding and activation assays across the melanocortin receptor family (MC1R through MC4R), where its receptor-selectivity profile makes it a useful probe for structure–activity work on α-MSH analogues.

Its lactam-bridged ring also makes it a model compound in cyclic-peptide stability and degradation studies, and it serves as an analytical reference standard. These are in vitro research applications only, and no medical claims are made here.

Lyophilized peptides are generally kept cold, dry, and out of light to preserve stability. PT-141 is stored long-term at -20°C (-4°F), protected from moisture and direct light, with original labeling retained so the batch stays traceable.

This overview does not cover preparation or use of any kind. That falls outside laboratory research reference use, and we do not provide that guidance.

Cyclic peptides bring their own failure modes: a ring-opened (linear) impurity or an incomplete lactam closure can sit close to the parent peak in a chromatogram while being a different molecule. Purity by HPLC and identity by mass spectrometry answer two different questions, and a serious report carries both.

This is why a per-batch Certificate of Analysis, one tied to the exact lot you receive, is more useful than a generic brand-level document.

Before relying on any batch, confirm three things: purity (an HPLC percentage), identity (a mass-spectrometry confirmation), and a traceable lot number with a test date. If the supplier lets you look up that batch’s report, you can match the documentation to the vial in hand.

See our guide on how to read a peptide COA for a field-by-field walkthrough.

Is PT-141 FDA approved? Bremelanotide, the peptide itself, is the active ingredient of an FDA-approved prescription drug (marketed as Vyleesi). The material described here is not that drug product and is not a substitute for it: it is a laboratory reference standard supplied strictly for analytical and in vitro research, and nothing on this site is medical guidance.

How does PT-141 relate to Melanotan II? PT-141 is a metabolite of Melanotan II in which the C-terminal amide is replaced by a free acid. Analytically they are distinct molecules with different masses, which is exactly the kind of difference mass-spectrometry identity testing exists to catch.

Is PT-141 legal in the US? Bremelanotide is not a scheduled substance under the Controlled Substances Act. It is lawfully supplied as a reference material for laboratory research, and for no other purpose; nothing on this site should be read as a claim otherwise.

Why a lyophilized vial and not another format? Reference material is quantified by mass and stability-characterised in lyophilized form, which is what a per-batch certificate can actually describe. Other formats fall outside laboratory reference use, so we do not offer them.