Cyclic heptapeptide melanocortin receptor agonist. FDA-approved as Vyleesi. Acts on central nervous system MC3R/MC4R receptors. Used as-needed with a rapid onset and short duration of action.
PT-141, known by its generic name bremelanotide, is a synthetic cyclic heptapeptide that acts as an agonist at melanocortin receptors MC3R and MC4R in the central nervous system. It is the only FDA-approved melanocortin receptor agonist of its kind, marketed under the brand name Vyleesi.
Unlike most peptides tracked in Milligram, PT-141 is not used on a daily or scheduled basis. It is an event-driven, as-needed compound with a rapid onset (peak within ~1 hour) and a short pharmacokinetic window (~8 hours total duration). This makes it pharmacologically distinct from long-acting compounds like testosterone esters or GLP-1 agonists.
PT-141 was derived from melanotan II but engineered for greater receptor selectivity. While melanotan II activates a broad range of melanocortin receptors (including MC1R, which drives melanogenesis/tanning), PT-141 is substantially more selective for the MC3R and MC4R subtypes, with minimal tanning effects.
PT-141 activates melanocortin-3 (MC3R) and melanocortin-4 (MC4R) receptors located primarily in the hypothalamus and limbic system. These receptors are part of the central melanocortin pathway — a neuroendocrine signaling system involved in energy homeostasis, autonomic function, and behavioral regulation.
PT-141 acts centrally (in the brain), not peripherally. This distinguishes it from compounds that work at the tissue level. The melanocortin system in the hypothalamus modulates autonomic nervous system signaling, which produces its downstream physiological effects. The effects are mediated by neural pathways, not direct vascular or hormonal mechanisms.
PT-141 demonstrates rapid absorption after subcutaneous injection, reaching peak plasma concentrations (Cmax) within approximately 1 hour. The terminal half-life is approximately 2.5 hours, which places it in the "short-acting" category alongside compounds like BPC-157 and GHK-Cu. However, its pharmacodynamic effects extend beyond the plasma half-life, with reported durations of 6–8 hours.
| Parameter | Value |
|---|---|
| Terminal Half-Life | ~2.5 hours |
| Time to Peak (Tmax) | ~1 hour post-injection |
| Bioavailability (SubQ) | ~95% |
| Duration of Action | ~6–8 hours |
| Dosing Pattern | As-needed (not daily) |
| Minimum Interval | 24 hours between doses |
| Maximum Frequency | 8 doses per month (FDA label) |
The 2.5-hour plasma half-life measures how quickly the peptide is cleared from the blood — but the physiological effects initiated by MC3R/MC4R activation in the CNS persist well beyond plasma clearance. This is common with centrally-acting peptides: the neural cascade triggered by receptor binding outlasts the presence of the compound in circulation.
PT-141 is an as-needed compound, not a daily protocol. Commonly reported dosing parameters:
Because PT-141 is not taken on a fixed schedule, tracking each dose with a timestamp is especially useful for maintaining the 24-hour minimum interval and staying within the monthly frequency limit. Milligram logs each dose event and tracks your usage pattern over time.
Lyophilized PT-141 peptide vials (typically 10 mg) require reconstitution with bacteriostatic water before use. Follow these steps for proper preparation:
You will need: PT-141 lyophilized vial (10 mg typical), bacteriostatic water (BAC water), alcohol swabs, and insulin syringes (29–31 gauge).
Swab the rubber stoppers of both the PT-141 vial and the BAC water vial with alcohol pads. Allow to air dry for a few seconds.
Draw 1–2 mL of BAC water into the syringe. For a 10 mg vial with 2 mL BAC water, each 0.1 mL (10 units on an insulin syringe) contains 0.5 mg of PT-141.
Insert the needle into the PT-141 vial and let the water run down the inside of the glass wall — do not spray directly onto the lyophilized cake. This prevents denaturing the peptide.
Swirl the vial gently until the peptide is fully dissolved. Do not shake. The solution should be clear and colorless. If cloudy or particulate, discard.
Store the reconstituted vial in the refrigerator (2–8°C). For a 1.75 mg dose from a 10 mg/2 mL solution, draw 0.35 mL (35 units). Use within 28 days of reconstitution.