# PT-141: Central Melanocortin Agonist — A Lab-Notebook Research Digest > PT-141 (bremelanotide) is a melanocortin MC4R/MC3R agonist that acts centrally, in the brain, not on blood flow. A cited, terse digest of the receptor pharmacology and the trial record. Receptor: MC4R, with MC3R secondary. Action: central. Approved use: premenopausal HSDD in women only. Everything else is off-label or research. Each figure is logged to its source. ## The short version PT-141 is a lab name for bremelanotide. It is a small, ring-shaped peptide — a short chain of amino acids joined in a loop. It switches on melanocortin receptors (docking sites for a natural brain signal) of the MC4R and MC3R types, which sit mostly in the brain. So PT-141 works in the brain, on the circuits behind sexual desire — not in the blood vessels the way the common erectile-dysfunction pills do [1][7]. One form of this peptide is an approved prescription drug for women before menopause who have low sexual desire that distresses them, a condition doctors call HSDD [3][7]. It is **not** approved for men, for women after menopause, or for performance, and it does not raise testosterone [9]. The most common effect people report in trials is nausea [4]. Material sold as a 'PT-141 research chemical' is not the approved drug. What people report — including the downsides like nausea and headache — is summarized on [PT-141 effects](/effects), and the receptor-level detail is on [PT-141 mechanism of action](/mechanism-of-action). ## What is PT-141 PT-141 is bremelanotide. Chemically: a synthetic cyclic heptapeptide — seven amino acids closed into a ring by a lactam bridge — modeled on alpha-MSH, an endogenous melanocortin signal the body makes from the precursor protein POMC [1][12]. Molecular weight ~1025.2 Da. CAS 189691-06-3. It is a structural relative of melanotan-II, developed by Palatin Technologies [12]. The ring matters. A cyclic peptide resists breakdown better than a linear chain, which is why PT-141 is stable enough to dose by injection [7]. The compound is a [melanocortin receptor agonist](/how-it-works): it binds melanocortin receptors and turns them on, chiefly MC4R [1]. Function follows the receptor. MC4R sits in hypothalamic and limbic circuits — the brain regions that set sexual motivation. Activate MC4R there, and downstream dopamine signaling tied to desire is engaged [5][11]. This is the central mechanism this site documents. ## PT-141 peptide The PT-141 peptide is defined by its sequence and its target. Sequence: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. Formula: C50H68N14O10. It differs from its parent melanotan-II by carrying a carboxylic acid where melanotan-II carries an amide [1]. The target is the melanocortin receptor family — five G-protein-coupled receptors, MC1R through MC5R. PT-141 acts on the central pair, MC4R and MC3R [1]. The first reported pharmacology, across rats and nonhuman primates, showed systemic dosing produced dose-dependent penile erections and activated hypothalamic neurons (measured as increased c-Fos, a marker of neuron firing) — direct evidence the peptide works through the brain [1]. In female-rat work the same peptide selectively raised solicitational (desire-driven) sexual behavior without changing reflexive behavior or general movement — the first agent reported to act on appetitive female sexual behavior [2]. ## Central action, not vascular The defining fact: PT-141 acts centrally. PDE-5 inhibitors (the common erectile-dysfunction class) work peripherally, on vascular smooth muscle, to improve blood flow. PT-141 does not act on vascular smooth muscle at all [10]. It acts on hypothalamic and preoptic neurons that govern the *desire* circuit upstream of any blood-flow event [1][10]. The human-imaging evidence is direct. In a crossover fMRI study of 31 premenopausal women with HSDD, MC4R agonism increased sexual desire for up to 24 hours and changed task-based brain processing of erotic stimuli — enhanced amygdala-insula connectivity and altered cerebellar activity [5]. That is a brain-level signal, not a vascular one. The full receptor-to-circuit account is on [PT-141 mechanism of action](/mechanism-of-action); the side-by-side with peripheral agents is on [how it works](/how-it-works). ## Status, plainly PT-141 / bremelanotide was approved in the United States on June 21, 2019 (NDA 210557) as a subcutaneous injection for acquired, generalized HSDD in premenopausal women [7]. That is the only approved indication. Not approved: men, postmenopausal women, performance, appetite or metabolic use. Phase 2 erectile-dysfunction data exists in men but did not lead to approval [13]. A critical re-analysis argues the trial effects on desire and distress, while statistically significant, are small [14]. Nausea is common (~40% over long-term use) and a notable driver of stopping [4]. The label warns of transient blood-pressure increase and is contraindicated in uncontrolled hypertension or cardiovascular disease [7]. The research-chemical form sits outside this approval framework entirely — no regulatory oversight of identity, purity, or concentration [9]. Read the caveats first: [PT-141 effects](/effects). --- A two-ink lab-notebook digest of the PT-141 (bremelanotide) record — the central MC4R mechanism, the premenopausal-HSDD-only approval, and the nausea-led tolerability cost logged to source and overprinted in plain sight, with the research-chemical form kept clearly off-register from the approved drug; no clinic behind the press and nothing here dosed, dispensed, or sold.