Research readout · Melanocortin MC4R agonist
PT-141 is a melanocortin MC4R agonist measured across the HSDD trials, with its tolerability read first.
Bremelanotide is approved for exactly one population on exactly one regimen. This is the measured record: what the trials confirmed, what reviewers dispute, and the side effects researchers actually encounter, every number cited.
The short version
PT-141 is the research name for bremelanotide, a small lab-made peptide that activates brain receptors tied to sexual desire. The FDA approved it in 2019 for one thing only: HSDD (hypoactive sexual desire disorder — persistent low sexual desire that causes real personal distress) in premenopausal women. It works in the brain, not on blood flow. The benefit in the trials is real but small. The most common problem is nausea, and a transient rise in blood pressure means it is off-limits for people with uncontrolled hypertension or heart disease. Every other use — in men, for erectile dysfunction — is off-label.
What Is PT-141?
PT-141 is the development designation for bremelanotide, a synthetic cyclic heptapeptide (a ring of seven amino acids) that acts as a melanocortin MC3R/MC4R receptor agonist — a compound that switches on the melanocortin MC3R/MC4R receptors (brain switches that influence sexual desire, appetite, and skin pigment) [6]. Its full sequence is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, molecular weight 1025.2 Da, formula C50H68N14O10, CAS 189691-06-3 [1]. It is a synthetic analogue of alpha-MSH, an endogenous melanocortin peptide the body makes from a precursor protein called POMC.
The single approved use is acquired, generalized HSDD in premenopausal women, under NDA 210557, approved June 21, 2019 [6]. That approval is the spine of this site. Everything else — use in men, in postmenopausal women, or for erectile function — is off-label, and the male/erectile evidence remains early-phase. Material sold as "PT-141 research chemical" is for laboratory use only; it is not the approved finished drug product.
What Is PT-141 Peptide?
The PT-141 peptide is a cyclic lactam analogue of alpha-melanocyte-stimulating hormone (alpha-MSH) — seven amino acids joined in a closed ring, stabilized by a lactam bridge between the Asp and Lys side chains [1]. The ring matters: a cyclic heptapeptide resists breakdown better than a linear one, which is part of why bremelanotide is dosable as a subcutaneous (injected just under the skin) drug while many linear peptides are not [6].
Structurally it is a relative of melanotan II, with the C-terminal amide swapped for a carboxylic acid. The result is a melanocortin receptor agonist whose primary action sits in the central nervous system — the basis for how PT-141 works in the brain. The terminal half-life after subcutaneous dosing is about 2.7 h (range 1.9-4.0 h) per the US prescribing information [6].
What Does the PT-141 Peptide Do?
PT-141 activates melanocortin MC3R/MC4R receptors concentrated in the hypothalamus and limbic system, engaging brain circuits for sexual desire and arousal [1]. In a controlled fMRI study of premenopausal women with HSDD, MC4R agonism altered how the brain processed erotic stimuli and increased reported sexual desire for up to 24 hours after a single dose [5]. That is the defining mechanistic distinction: it works centrally, through the neural circuitry of desire, rather than peripherally on vascular smooth muscle the way PDE-5 inhibitors do.
In the two pivotal Phase 3 trials (RECONNECT, n=1267), the 1.75 mg as-needed subcutaneous regimen met both coprimary endpoints — desire rose and desire-related distress fell versus placebo [3]. The size of that benefit is genuinely modest and openly contested, which is the subject of the effect-size debate.
What Is PT-141 Used For?
Its single FDA-approved use is acquired, generalized hypoactive sexual desire disorder (HSDD) in premenopausal women [6]. "Acquired" means the low desire is a change from a prior baseline; "generalized" means it is not limited to a specific partner or situation; and HSDD requires that the low desire cause marked personal distress [3].
Use in men, for erectile dysfunction, or in postmenopausal women is off-label. For the male and erectile setting the evidence is early-phase and investigational — there is no approval and the data are limited, which is why PT-141 for men (off-label research) is scoped strictly as research. The compound does not act through the HPG axis and does not directly raise testosterone, and it is not a PDE-5 inhibitor [11]. The honest tolerability picture — led by nausea — is covered under PT-141 side effects.