PT-141 (Bremelanotide) — the melanocortin-receptor agonist, explained
PT-141 (bremelanotide) is a synthetic 7-amino-acid peptide that activates melanocortin receptors, primarily MC3R and MC4R. It has an unusually well-documented research development history — the molecule descends from Melanotan II research at the University of Arizona in the 1990s. This primer covers the molecule, the melanocortin receptor system, the published literature, the Phase III trial evidence base, and what researchers should know before working with it.
The molecule. PT-141 (bremelanotide) is a cyclic 7-amino-acid peptide with sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. Molecular weight is approximately 1025 Da (free acid form, slightly higher for the acetate salt commonly supplied). The cyclization produces a constrained structure that gives selectivity for central melanocortin receptors over peripheral pathways. PT-141 is derived from Melanotan II, the original α-MSH analog developed by Hadley and Levine at the University of Arizona for tanning research — PT-141 is the truncated, cyclized variant optimized for selective MC3R/MC4R agonism without the tanning-related effects of peripheral MC1R activation.
The melanocortin system. The melanocortin receptors are a family of five G-protein-coupled receptors (MC1R-MC5R) with distinct tissue distributions and physiological roles. MC1R is the pigmentation receptor (on melanocytes). MC2R is the ACTH receptor (on adrenal cortex). MC3R and MC4R are primarily central nervous system receptors involved in energy homeostasis, sexual behavior, and autonomic function. MC5R is on exocrine glands. PT-141 has highest affinity for MC3R and MC4R, which produces the sexual-behavior effects without significant pigmentation or adrenal effects. The molecule crosses the blood-brain barrier sufficiently to engage central MC3R/MC4R populations.
Published literature — primary sources. The key narrative review is King SH et al. Mechanism of action of bremelanotide on the central nervous system: a narrative review. Int J Womens Health. 2018;10:711-719. For the original mechanism work, Molinoff PB et al. PT-141: a melanocortin agonist for the treatment of sexual dysfunction. Ann N Y Acad Sci. 2003;994:96-102 is the Palatin discovery-era paper. The Phase III RECONNECT trials are reported in Kingsberg SA et al. Bremelanotide for the Treatment of Hypoactive Sexual Desire Disorder: Two Randomized Phase 3 Trials. Obstet Gynecol. 2019;134(5):899-908 — the primary Phase III evidence base.
What's been studied. The Phase III evidence base is the RECONNECT-1 and RECONNECT-2 trials. Earlier clinical work examined other central-nervous-system pharmacology endpoints, and mechanistic research has included hemorrhagic-shock models (where melanocortin agonism modulates blood pressure). The research literature spans a broader range of central-nervous-system pharmacology than the Phase III program alone captures.
Administration routes and dose ranges. The approved Vyleesi product is a 1.75 mg subcutaneous injection via autoinjector, administered approximately 45 minutes before anticipated sexual activity, no more than once per 24 hours, not more than 8 times per month. Research protocols have used similar or slightly higher doses (2-4 mg). The intranasal route has been studied in earlier erectile-dysfunction work. Subcutaneous is the dominant research route. Published pharmacokinetics show peak plasma concentration at ~1 hour post-injection and clearance over 6-8 hours.
Side effect profile — worth understanding. Published trial data shows PT-141's most common adverse effects are nausea (~40% of trial participants), flushing (~20%), headache, and injection-site reactions. Blood pressure elevation (transient, ~6/3 mmHg) is a labeled warning for Vyleesi and is relevant in research contexts — participants with uncontrolled hypertension are excluded from the approved indication. Skin hyperpigmentation has been reported rarely, consistent with some residual MC1R activity at higher doses.
Storage, stability, and handling. PT-141 in a prefilled pen is stable at 2–8 °C through the labeled expiry date. The Vyleesi commercial product has a room-temperature excursion tolerance per labeling (up to 90 days at ≤ 25 °C once in use), but research-grade material in pen format should generally be maintained at 2–8 °C except during administration. Do not freeze. Protect from light.
What the COA should say. A batch-specific COA for PT-141 should include (1) identity confirmation by HPLC-MS against the theoretical mass (~1025 Da for free acid), (2) purity by reverse-phase HPLC-UV at 214 nm ≥ 98.0%, (3) residual solvent profile per ICH Q3C, (4) endotoxin by LAL in EU/mg. The cyclization bridge between Asp and Lys is a synthesis yield-critical step — a purity chromatogram with shoulder peaks near the main peak can indicate incomplete or mis-cyclized variants, which are not biologically equivalent.
Research-use only. Vivaprime supplies PT-141 (bremelanotide) as research reference material for qualified researchers engaged in in-vitro laboratory work. The research-grade material supplied here is not a pharmaceutical-grade product and is not supplied with the release documentation required for clinical or patient-facing use. Nothing on this page constitutes a therapeutic, diagnostic, or consumption recommendation. Purchasers affirm the research-use agreement at checkout.