Research documentation · Bremelanotide · Melanocortin agonist
PT-141 is the research designation for bremelanotide, an approved melanocortin receptor agonist studied for sexual desire.
An FDA-approved drug whose approval covers exactly one indication — acquired, generalized HSDD in premenopausal women — and everything else is off-label. Every clinical number here is cited; the field reports are fenced off from the evidence.
The short version
PT-141 is the research name for bremelanotide, a small lab-made peptide (a short chain of amino acids) that acts on switches in the brain rather than on blood flow. The US FDA approved it in June 2019 — but only for one thing: HSDD (hypoactive sexual desire disorder — persistent low sexual desire that causes real personal distress) in premenopausal women. In the approval trials it raised desire by a real but modest amount. Using it in men, for erectile problems, or after menopause is off-label — not what the approval covers, and backed only by early studies. This page covers what PT-141 is, how it works, and where that line sits.
What PT-141 actually is
PT-141 is bremelanotide: a synthetic cyclic heptapeptide (a ring of seven amino acids) that activates central melanocortin receptors, chiefly MC4R [1][6]. Its sequence is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, molecular weight 1025.2 Da, formula C50H68N14O10, CAS 189691-06-3 [6]. It is a structural relative of melanotan II, but with the C-terminal amide replaced by a carboxylic acid [1].
The distinction that matters most for a reader doing due diligence: bremelanotide is a real, approved prescription drug — approved under NDA 210557 in June 2019 [6]. It is not an unapproved "research chemical" in the regulatory sense the way many portfolio compounds are. What is true is that the approval is narrow, and that material sold online as "PT-141 research chemical" is laboratory material outside the pharmaceutical framework — no oversight of identity, purity, or concentration [5]. The two should not be confused.
Unlike PDE-5 inhibitors (the sildenafil/tadalafil class), which act peripherally on vascular smooth muscle to improve blood flow, PT-141 works centrally on the brain circuits of sexual motivation [1]. It does not act through the HPG axis and does not directly raise testosterone — a common misconception [5].
PT-141 Peptide: A Synthetic Melanocortin Analogue
As a peptide, the PT-141 peptide is a seven-amino-acid cyclic lactam analogue of alpha-MSH (alpha-melanocyte-stimulating hormone — a natural brain peptide cut from a larger precursor protein, POMC) [1]. The cyclic ring is not cosmetic: closing the chain into a lactam loop makes the molecule more stable than the linear melanocortin peptides it descends from, which is part of why it survived into a viable injectable drug.
In animal pharmacology, systemic PT-141 produced erections in rats and nonhuman primates and lit up hypothalamic neurons (measured as increased c-Fos), evidence of a central — brain-level — site of action rather than a local vascular one [1]. In female rats it selectively increased appetitive, solicitational sexual behavior (the proceptive, desire-driven kind) without changing reflexive behaviors or general movement — the first pharmacological agent reported to do so [2]. Those two preclinical lines are the foundation the human program was built on.
What a Melanocortin Receptor Agonist Is
A melanocortin receptor agonist is a compound that switches on the melanocortin receptor family (MC1R through MC5R), the same receptors that respond to the body's own alpha-MSH [1]. PT-141 targets the central subtypes: chiefly MC4R, with secondary MC3R activity [6]. MC4R sits in hypothalamic circuits — including the medial preoptic area — that govern both sexual desire and appetite, which is why high-frequency dosing in early studies also touched caloric intake [4][6].
The same receptor family explains a known cosmetic effect: peripheral MC1R activation drives melanin production, so repeated frequent dosing can darken skin, gums, and other tissue (hyperpigmentation) [5]. A 2022 fMRI study in 31 premenopausal women with HSDD gave the mechanism a human readout — MC4R agonism increased sexual desire for up to 24 hours and altered task-based brain processing of erotic stimuli, including enhanced amygdala-insula connectivity [13]. That is how PT-141 works in one line: a central melanocortin switch, not a blood-flow drug.
PT-141 for Men: Off-Label and Investigational Only
PT-141 for men is off-label. The approval covers premenopausal women with HSDD and no one else [6]. The male/erectile story is real but early: the original Molinoff program reported rapid, dose-dependent erectile activity in men with erectile dysfunction, and early intranasal dose-escalation studies found a statistically significant erectile response above roughly 7 mg [1]. That is investigational, early-phase evidence — not an approved use, and it should be read as such.
One specific caution for anyone surveying the male literature: a 2008 erectile-dysfunction "salvage" study (Safarinejad & Hosseini) received a formal Expression of Concern in 2023, meaning its integrity is in question; treat its findings as disputed [5]. The honest summary is that PT-141's effect in men is biologically plausible and was observed in early trials, but it has never been carried to approval, and the cleanest evidence base — the one the FDA actually acted on — is entirely in women.
Is PT-141 FDA-Approved?
Yes — with a precise scope. As bremelanotide, PT-141 is FDA-approved (NDA 210557, June 21, 2019) for acquired, generalized HSDD in premenopausal women, given as a 1.75 mg subcutaneous (injected just under the skin) injection as needed [5][6]. That is the entire approved indication.
Everything else — use in men, for erectile dysfunction, or in postmenopausal women — is off-label and not supported by the approval [6]. PT-141 is not a US controlled or scheduled substance. Under anti-doping rules it falls within the WADA non-approved-substances framework (S0); athletes should consult current WADA guidance directly. For the full evidence picture, see the PT-141 clinical trials and the PT-141 side effects, or jump straight to the research references.