PT-141 (Bremelanotide) is a synthetic heptapeptide analogue derived from Melanotan II. Unlike the broader MT-II profile that activates multiple melanocortin receptors, PT-141 was engineered with a focus on MC4R activity in central nervous system pathways. The pharmacology is distinct and the clinical research record is unusual — it became the first MC4R-targeting therapeutic approved for hypoactive sexual desire disorder. This article maps the research.
Structure and selectivity
PT-141 sequence: Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-OH. The structural difference from Melanotan II is removal of the C-terminal amide. This subtle change shifts the receptor profile — PT-141 activates MC4R more selectively in central pathways while showing reduced melanogenic activity (MC1R-mediated skin pigmentation).
Mechanism — central MC4R activation
MC4R is densely expressed in the hypothalamus, brainstem, and limbic regions. Activation modulates:
- Sexual arousal pathways (specifically the medial preoptic area and paraventricular nucleus)
- Appetite signalling (less relevant for the PT-141 use case)
- Autonomic tone and cardiovascular regulation
PT-141 produces sexual response effects through CNS pathways rather than peripheral vascular action — distinguishing it mechanistically from PDE5 inhibitors which act on penile vasculature.
Clinical research record — hypoactive sexual desire disorder
The RECONNECT trial programme (Kingsberg et al., 2019) examined PT-141 in premenopausal women with hypoactive sexual desire disorder. Results showed statistically significant improvement in desire scores compared with placebo over 24 weeks. The FDA approved bremelanotide in 2019 under the brand name Vyleesi for this specific indication.
Mechanism of action vs PDE5 inhibitors
| Compound class | Mechanism | Site of action |
|---|---|---|
| PDE5 inhibitors (sildenafil) | Vascular cGMP enhancement | Peripheral (penile vasculature) |
| PT-141 / Bremelanotide | MC4R agonism | Central (hypothalamus, brainstem) |
The mechanism distinction means PT-141 functions in research populations where PDE5 inhibitors are inadequate or contraindicated.
Side effect profile in trials
The most-reported adverse events in clinical trials:
- Nausea (~40% of subjects, mild-to-moderate)
- Flushing
- Headache
- Transient blood pressure elevation (typically <10 mmHg, dose-dependent)
The transient blood pressure elevation is a notable mechanism-related effect — MC4R activation in autonomic centres affects vascular tone.
PT-141 vs Melanotan II
The two peptides share the same melanocortin family but with distinct profiles:
| Attribute | PT-141 | Melanotan II |
|---|---|---|
| MC1R activation | Low | High (melanogenesis) |
| MC4R activation | High (selective focus) | High (non-selective) |
| MC3R/MC5R | Lower | Higher |
| Skin pigmentation | Minimal | Pronounced |
Pharmacokinetic profile
- Subcutaneous bioavailability: ~80%
- Plasma half-life: ~2 hours
- Onset of effect: ~45 minutes to peak
- Duration of central effect: ~4-6 hours
Stability and reconstitution
PT-141 is supplied lyophilised. Reconstitution in bacteriostatic water at 1–2 mg/mL is standard. The cyclic backbone provides good stability. Refrigerated reconstituted PT-141 retains potency for approximately 4 weeks.
Research applications
- MC4R pathway pharmacology
- CNS sexual response circuit studies
- Melanocortin family receptor specificity research
- Autonomic regulation models
Chempeptides supplies HPLC-verified PT-141 with batch CoA — see the catalogue and our Melanotan II article for the broader melanocortin family.
Research use only.