This is a working overview of bremelanotide, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-02-14 and is reviewed periodically as new material appears.
Bremelanotide acts as an agonist at melanocortin receptors, a family of five G-protein-coupled receptors labeled MC1 through MC5. Binding studies indicate activity at several of these subtypes rather than strict selectivity for one. Signalling proceeds mainly through Gs-mediated activation of adenylyl cyclase, raising intracellular cyclic AMP. The MC4 receptor, expressed in hypothalamic and limbic circuits, is widely regarded as the subtype most relevant to sexual response. Because the molecule is not subtype-selective, effects at other melanocortin receptors are expected and are used to explain some observed side effects.
The peptide contains seven amino acids arranged in a ring, closed by a lactam bridge between a side-chain acid and an amine. This cyclic constraint holds the backbone in a defined conformation and increases resistance to enzymatic breakdown relative to linear analogs. N-terminal acetylation and a C-terminal amide further protect the molecule from exopeptidases. The result is a compound with a comparatively long circulation time for a small peptide. Structural modification of the bridge alters receptor affinity, which is one reason analogs in this family differ in their subtype preferences.
Activation of MC4R in the hypothalamus is thought to influence dopaminergic signaling, which in turn affects arousal and desire. This mechanism differs from that of phosphodiesterase type 5 inhibitors, which act primarily on vascular smooth muscle in the genital region. Because the pathway is central rather than peripheral, effects are not strictly dependent on local blood flow. The precise downstream cascade linking receptor binding to behavioral outcomes remains an area of ongoing investigation.
Clinical development of bremelanotide proceeded through several reformulation attempts. An early intranasal version was discontinued, and a subcutaneous auto-injector formulation later received approval for hypoactive sexual desire disorder in premenopausal women. Approval decisions have varied by country and over time, and the product has not been universally adopted. Blood pressure elevation is a documented effect, which is why some jurisdictions require monitoring after administration. The clinical evidence base continues to evolve as additional studies are published.
| Property | Value | Notes |
|---|---|---|
| Primary receptor family | Melanocortin (MC1 to MC5) | Agonist activity reported at several subtypes |
| Signalling pathway | Gs, adenylyl cyclase, cyclic AMP | Canonical melanocortin signalling route |
| Backbone length | Seven amino acids | Classified as a cyclic heptapeptide |
| Ring closure | Lactam bridge | Constrains conformation and resists peptidases |
| Terminal modifications | Acetylated N-terminus, amidated C-terminus | Reduces breakdown by exopeptidases |
Development of the peptide passed through several delivery formats, including an intranasal version tested in early trials and an injectable version that entered later clinical study. Regulatory approval for a subcutaneous product in the United States was granted in 2019 after review of controlled trials in premenopausal women. Outside the clinic, the compound circulates in research and non-pharmaceutical markets under its code name, where identity and purity vary considerably between suppliers. Synonyms appearing across technical literature include bremelanotide, PT-141, and Palatin 141.
PT-141 is the research designation for bremelanotide, a synthetic cyclic heptapeptide developed as a melanocortin receptor agonist. The peptide contains seven amino acids with an internal lactam bridge that constrains the backbone into a stable ring. Cyclisation of this kind improves resistance to enzymatic degradation relative to linear analogues. The compound was first explored for effects on melanin production, because several melanocortin receptors influence pigmentation. Its later association with sexual desire emerged from observations made during that early work, and the molecule became the subject of a separate development programme.
Bremelanotide is a moderately large peptide with a molecular mass near 1025 daltons. In lyophilised form it appears as a white to off-white powder and is freely soluble in water and other polar solvents. The intact lactam ring is essential for receptor affinity, while linearised fragments bind far more weakly. Solutions are sensitive to extremes of pH and to prolonged exposure to light and heat, so handling typically involves buffered conditions and cold storage. Its short plasma half-life reflects rapid distribution and clearance rather than chemical breakdown inside the vial.
The compound emerged from a research programme examining melanocortin analogues for effects on skin pigmentation. During early human studies, participants reported spontaneous erections as an unexpected side effect, which redirected development toward sexual function rather than tanning. An intranasal formulation was investigated in clinical trials but did not reach market approval. A subcutaneous injectable version later completed the regulatory process, and the nasal route does not appear in approved labelling.
Approved use is narrow and jurisdiction-specific. In the United States, the injectable product is authorised for premenopausal women with acquired, generalised hypoactive sexual desire disorder, a diagnosis that requires documented distress. It is not approved for men, for postmenopausal women, or for use alongside hormonal contraceptives under the approved labelling. Outside regulated markets, the same peptide is frequently sold as a research chemical, where identity, purity, and sterility are not independently verified.
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=== Chemical === The chemistry of astatine is "clouded by the extremely low concentrations at which astatine experiments have been conducted, and the possibility of reactions with impurities, walls and filters, or radioactivity by-products, and other unwanted nano-scale interactions". Many of its apparent chemical properties have been observed using tracer studies on extremely dilute astatine solutions, typically less than 10−10 mol dm−3. Some properties, such as anion formation, align with other halogens. Astatine has some metallic characteristics as well, such as plating onto a cathode, and coprecipitating with metal sulfides in hydrochloric acid. It forms complexes with EDTA, a metal chelating agent, and is capable of acting as a metal in antibody radiolabeling; in some respects, astatine in the +1 state is akin to silver in the same state. Most of the organic chemistry of astatine is, however, analogous to that of iodine. It has been suggested that astatine can form a stable monatomic cation in aqueous solution. Astatine has an electronegativity of 2.2 on the revised Pauling scale—lower than that of iodine (2.66) and the same as hydrogen. In hydrogen astatide (HAt), the negative charge is predicted to be on the hydrogen atom, implying that this compound could be referred to as astatine hydride according to certain nomenclatures. That would be consistent with the electronegativity of astatine on the Allred–Rochow scale (1.9) being less than that of hydrogen (2.2).
A safety review reported that deaths from tyramine/MAOI-induced hypertension are extremely rare and that no deaths from MAOI-induced hypertension had been reported in the medical literature for several decades. Phenelzine should not be combined with drugs that have significant serotonin reuptake inhibition or significant serotonin-releasing activity, because of the risk of serotonin toxicity. Examples include selective serotonin reuptake inhibitors (SSRIs), serotonin–norepinephrine reuptake inhibitors (SNRIs), clomipramine, imipramine, MDMA, and certain analgesics such as meperidine, tramadol, methadone, tapentadol, dextromethorphan, dextropropoxyphene, pentazocine, and levorphanol. This serotonin-toxicity mechanism is distinct from the usual caution about overlapping MAO-inhibiting agents. Classic MAOI-to-classic MAOI overlap is not expected to cause serotonin toxicity by itself, although routine long-term coadministration is generally avoided because of limited safety data and lack of usual therapeutic rationale. Indirect monoamine-releasing sympathomimetics without significant serotonergic activity, such as ephedrine and pseudoephedrine, are not absolute contraindications, but may increase blood pressure and are generally avoided or used only cautiously at reduced doses with monitoring. Pseudoephedrine is considered less potent than ephedrine, and ephedrine less potent than amphetamine.
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Sources: en.wikipedia.org
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== Molecular structure == Biochemically, the indoleamine molecule derives from the amino acid tryptophan, via the (rate-limiting) hydroxylation of the 5 position on the ring (forming the intermediate 5-hydroxytryptophan), and then decarboxylation to produce serotonin. Preferable conformations are defined via ethylamine chain, resulting in six different conformations.
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Sources: en.wikipedia.org
It is frequently described as an MC4 receptor agonist, but binding assays show activity at more than one melanocortin subtype. Selectivity is therefore relative rather than absolute. This matters when interpreting side effects tied to other receptor subtypes.
The lactam bridge locks the peptide into a defined shape and makes it harder for peptidases to cut the backbone. Terminal blocking groups add further protection at both ends. Together these features extend the molecule's persistence in circulation compared with linear peptides.
Evidence from animals favors hypothalamic melanocortin circuits, yet direct confirmation in humans is lacking. A peripheral vascular contribution has also been proposed. How receptor binding translates into a reported behavioral effect is still not mapped.
PT-141 is the research code for bremelanotide, a cyclic peptide developed as a melanocortin receptor agonist. The code has appeared in literature and catalog listings since early development. Bremelanotide is the international nonproprietary name.