PT-141 (bremelanotide) is a cyclic heptapeptide metabolite of Melanotan II that has been refined for MC4R-biased agonism and received FDA approval for hypoactive sexual desire disorder; Melanotan II is the parent compound with broader receptor activity across MC1R, MC3R, MC4R, and MC5R, and remains an investigational research compound without regulatory approval.
Research reference only — all information on this page summarises peer-reviewed scientific literature and does not constitute medical advice. View full compound profiles: PT-141 · Melanotan II
Mechanism Comparison
PT-141 (bremelanotide) was discovered as the primary active metabolite of Melanotan II following in vivo deacetylation at the N-terminus (removal of the acetyl group). Both are cyclic lactam heptapeptides sharing the core Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂ scaffold; PT-141 is distinguished by the absence of the N-terminal acetyl group (H-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂). This structural change confers relative selectivity toward MC4R and MC3R over MC1R, reducing the pigmentation-driving MC1R activity while preserving the central MC4R-mediated sexual arousal signalling. MC4R activation in the paraventricular nucleus and medial preoptic area drives downstream nitric oxide (NO) signalling, producing the pro-erectile and pro-sexual effects characterised in clinical trials. Melanotan II engages all four of these receptors with approximately equal potency, producing the full melanocortin spectrum including melanogenesis (MC1R), appetite suppression (MC4R/MC3R), sexual function (MC4R), and exocrine effects (MC5R). The deacetylation that converts Melanotan II to PT-141 in vivo is the metabolic basis for both compounds' sexual function activity — PT-141 is pharmacologically the active principle.
Side-by-Side Attributes
| Attribute | PT-141 | Melanotan II |
|---|---|---|
| Structural relationship | N-deacetylated metabolite of Melanotan II | Parent cyclic heptapeptide (N-acetylated) |
| CAS number | 189691-06-3 | 121062-08-6 |
| Molecular weight | ~1,025 Da (deacetylated) | ~1,024 Da (acetylated) |
| MC receptor selectivity | MC3R/MC4R-biased; reduced MC1R activity | Non-selective: MC1R, MC3R, MC4R, MC5R |
| Melanogenesis activity | Reduced (MC1R de-emphasised) | Present (MC1R activation drives pigmentation) |
| FDA regulatory status | FDA-approved — Vyleesi® (2019), HSDD in premenopausal women | Not approved; investigational research compound |
| Administration route | Subcutaneous auto-injector (1.75 mg) | Subcutaneous; no approved formulation |
| Key clinical trial | RECONNECT trials (Clayton et al., NEJM, 2019) | Phase 1/2 data (Diamond et al., 2004; 2005) |
| Primary research utility | MC4R sexual function biology; HSDD mechanism research | Broad melanocortin pharmacology; MC1R/MC4R comparison studies |
Key Research Points
- 1PT-141 (bremelanotide) was identified in the clinical development of Melanotan II when subjects in early melanogenesis trials reported unexpected penile erections. Subsequent research isolated PT-141 as the primary active metabolite and developed it specifically for sexual function — resulting in the first FDA-approved non-hormonal treatment for hypoactive sexual desire disorder (HSDD) in premenopausal women (Vyleesi®, June 2019).
- 2The structural difference between PT-141 and Melanotan II is a single acetyl group at the N-terminus: Melanotan II is N-acetylated (Ac-Nle-...), while PT-141 (bremelanotide) is the deacetylated form (H-Nle-...). This seemingly minor change shifts receptor selectivity, reducing relative MC1R activity and making PT-141 more biased toward MC3R/MC4R signalling relevant to sexual function.
- 3Both compounds act centrally (in the brain) rather than peripherally (in genital tissue). This is a pharmacologically important distinction from PDE5 inhibitors (sildenafil, tadalafil), which act peripherally on vascular smooth muscle. The central MC4R mechanism means PT-141 and Melanotan II require intact neural signalling from hypothalamus to periphery and can act on desire and arousal circuits, not just blood flow.
- 4The RECONNECT Phase 3 trials (Clayton et al., New England Journal of Medicine, 2019) demonstrated statistically significant improvements in satisfying sexual events (SSEs) and desire scores vs placebo in premenopausal women with HSDD. Nausea was the primary adverse event (40% of subjects), attributable to MC3R/MC4R activation in the area postrema. This same nausea mechanism applies to Melanotan II at similar receptor-occupancy levels.
- 5Researchers using Melanotan II as a tool compound should note that its MC1R activity confounds studies targeting only MC4R biology. PT-141 provides a cleaner MC4R/MC3R pharmacological tool when studying sexual function and appetite circuits, while Melanotan II is more appropriate for studies requiring simultaneous engagement of all four melanocortin receptor subtypes.
Frequently Asked Questions
What is the difference between PT-141 and Melanotan II?
PT-141 (bremelanotide) is the N-deacetylated metabolite of Melanotan II — the two compounds differ by a single acetyl group at the N-terminus. Both are cyclic heptapeptides targeting melanocortin receptors, but PT-141 shows relative selectivity for MC3R and MC4R with reduced MC1R activity, minimising the melanogenesis (skin darkening) effects prominent with Melanotan II. PT-141 (Vyleesi®) received FDA approval in 2019 for hypoactive sexual desire disorder in premenopausal women — making it the only FDA-approved agent in this drug class. Melanotan II remains an investigational research compound without regulatory approval.
Is PT-141 (bremelanotide) FDA approved?
Yes. Bremelanotide (Vyleesi®, AMAG Pharmaceuticals / Palatin Technologies) received FDA approval in June 2019 for the treatment of hypoactive sexual desire disorder (HSDD) in premenopausal women. It is administered as a 1.75 mg subcutaneous injection at least 45 minutes before anticipated sexual activity. The approval was based on the Phase 3 RECONNECT trials demonstrating statistically significant increases in satisfying sexual events and reductions in distress related to low sexual desire. It is not approved for use in postmenopausal women or men.
How does PT-141 produce its effects on sexual function?
PT-141 (bremelanotide) activates MC4R (melanocortin 4 receptor) in hypothalamic nuclei — specifically the paraventricular nucleus (PVN) and medial preoptic area (MPOA) — driving neuronal signalling cascades that increase sexual desire and arousal. Downstream, MC4R activation in these nuclei stimulates nitric oxide (NO) release, which signals via descending pathways to increase blood flow and arousal in peripheral genital tissue. This central mechanism is pharmacologically distinct from PDE5 inhibitors (sildenafil, tadalafil), which act peripherally on vascular smooth muscle without engaging desire circuits. PT-141's central action is proposed to explain its ability to increase subjective desire — not merely physiological arousal.
Deep Dive
For extended mechanism analysis, trial data, and regulatory context, see the full research article:
Melanocortin Peptides: MT-I, MT-II, and the MC Receptor System in Research →Full compound profile
PT-141
Full compound profile
Melanotan II