# PT-141 (Bremelanotide): What It Is, How It Works, and What the Trials Found > PT-141 is the research name for bremelanotide, a melanocortin MC3R/MC4R agonist FDA-approved in 2019 for HSDD in premenopausal women. A plain-English digest of the mechanism, the evidence, and the honest tolerability picture. Here is the whole story in plain English: what the molecule is, how it acts on the brain rather than blood flow, what the trials actually measured, and the honest side-effect picture — read first, not buried. ## The short version Here is PT-141 in a few lines. PT-141 is the research name for **bremelanotide**, a small synthetic peptide that works on the brain to influence sexual desire. It activates melanocortin MC3R/MC4R receptors (brain switches that influence sexual desire, appetite, and skin pigment) — so it acts on the *wanting*, not on blood flow. The US Food and Drug Administration approved it in June 2019, but for exactly one use: HSDD (hypoactive sexual desire disorder — persistent low sexual desire that causes real personal distress) in premenopausal women [6]. Every other use — in men, for erectile problems, in postmenopausal women — is off-label, and the male evidence is still early. The benefit in trials was real but modest, and the most common cost is nausea. That is the honest one-paragraph picture; the rest of this site is the detail, cited. ## What is PT-141? PT-141 is the development designation for bremelanotide, a synthetic cyclic heptapeptide (a ring of seven amino acids) modeled on a natural body signal called alpha-MSH (alpha-melanocyte-stimulating hormone — a hormone your body makes that switches on melanocortin receptors) [1]. Same molecule, two names: **PT-141** is the research label; **bremelanotide** is the official drug name (the international nonproprietary name, INN) carried on FDA approval NDA 210557 [6]. The approved product is a 1.75 mg shot given subcutaneously (injected just under the skin), used as needed in premenopausal women with HSDD [6]. Its single FDA-approved use is that one indication. Material sold online as a "PT-141 research chemical" is a separate, laboratory-only form — not the finished, approved medicine — with no regulatory oversight of its identity, purity, or strength. This site is an editorial digest of the published research and the approved label. It does not sell, supply, or recommend anything. The two facts people most often get wrong: PT-141 does not raise testosterone, and it is not a blood-flow drug. It works one rung up, on the brain's desire circuitry. We unpack both below and on the [central MC4R mechanism](/research) page. ## PT-141 Peptide: What the Compound Is As a molecule, the PT-141 peptide is a 1,025 Da cyclic seven-amino-acid lactam — sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, molecular formula C50H68N14O10, CAS 189691-06-3 [1]. The ring is closed by a lactam bridge between two side chains, and that cyclic shape makes it sturdier than a straight-chain peptide of the same length. Structurally, it is a close relative of an earlier melanocortin peptide, with the tail amide swapped for a carboxylic acid [1]. The practical upshot of the chemistry is range: because it is a compact, stable cyclic peptide, it survives long enough in the body to reach the central receptors it targets. The approved route is a single subcutaneous injection; an earlier nasal-spray version was studied and dropped because absorption was too variable [6]. Everything quantitative on this page — the dose, the timing, the half-life — comes from the published trials or the FDA label, never from this site's own protocol. ## What is a melanocortin receptor agonist? A melanocortin receptor agonist is a compound that switches *on* the body's melanocortin receptors — a family of five (MC1R through MC5R) that normally respond to natural signals like alpha-MSH [1]. PT-141 is one of these agonists, and it aims at the two central (brain) members of the family: MC4R and, secondarily, MC3R [1]. Which receptor it hits explains what it does — and what it doesn't. MC4R sits in brain circuits that govern sexual desire (and, separately, appetite), which is why the desire effect and the appetite/weight effects both trace back to the same receptor [6]. MC1R lives in the skin, which is why repeated, frequent dosing can darken skin and gums — a pigment effect, not a desire effect [6]. One molecule, several receptors, several different consequences: that is the whole logic of the compound in a sentence. ## What the PT-141 evidence actually shows The strongest evidence sits in two identical Phase 3 trials called RECONNECT, run in 1,267 premenopausal women with HSDD. The approved 1.75 mg as-needed shot beat placebo on both main scores — sexual desire rose (integrated FSFI-desire +0.35, P<.001) and the distress that low desire caused fell (integrated FSDS-DAO item 13 −0.33, P<.001) over 24 weeks [3]. Those are the numbers that won approval, and they are statistically real. They are also modest, and we say so plainly: an independent re-analysis argued the desire and distress effects are small and questioned how meaningful they are day to day [10]. Both things are true at once — a genuine signal, a modest size. A separate brain-imaging study helps explain the *how*: in 31 women, MC4R activation raised desire for up to 24 hours and changed how the brain processed erotic cues [5]. For the full evidence walk-through, including the mechanism and the off-label male research, see [the RECONNECT Phase 3 trials](/research). For the honest cost side — the full [tolerability and adverse events](/side-effects) record — read [PT-141 side effects](/side-effects), where we put tolerability up front, not in the footnotes. --- A bright, plain-English digest of the PT-141 (bremelanotide) record — the one approved use, the modest benefit, and the nausea-led tolerability cost read first and cited to source, with the community field reports kept squishily to one side and clearly marked unverified; a friendly reading desk, not a clinic, and nothing here dosed, sourced, or sold.