PT-141 / Bremelanotide: Research Overview

PT-141, the research-use name for bremelanotide, is a cyclic heptapeptide derived from the alpha-melanocyte-stimulating hormone (α-MSH) analog Melanotan II. Unlike its predecessor, PT-141 was developed specifically as a central nervous system-active compound without the potent tanning effects of non-selective melanocortin agonists. In 2019, the FDA approved bremelanotide under the trade name Vyleesi for the treatment of acquired, generalized hypoactive sexual desire disorder (HSDD) in premenopausal women — making it one of only two FDA-approved pharmacological treatments for female sexual dysfunction. Research-chemical vendors sell unlabeled bremelanotide powder for laboratory use under the PT-141 designation.

What is PT-141 / Bremelanotide?

Bremelanotide (PT-141) is a cyclized heptapeptide with a molecular weight of approximately 1025.18 Da. Its chemical structure is cyclo-[Nle4, Asp5, D-Phe7]-α-MSH(4-10), meaning it is a ring-constrained fragment of α-MSH modified for metabolic stability and receptor selectivity. The cyclization renders it resistant to rapid proteolytic degradation that would otherwise limit efficacy. As Vyleesi, it is formulated as an aqueous solution (1.75 mg/0.3 mL) in a prefilled autoinjector. As a research compound, it is typically supplied as a lyophilized powder in 5 mg or 10 mg vials. In the United States, Vyleesi is a prescription drug; research-peptide vendors sell unlabeled bremelanotide as a research compound.

Mechanism of Action

Bremelanotide is an agonist at melanocortin receptors 3 and 4 (MC3R and MC4R), which are expressed in the hypothalamus and other limbic brain regions. Activation of MC4R in the paraventricular nucleus and mesolimbic areas modulates neural pathways associated with sexual motivation and arousal — a mechanism that is entirely central (brain-based) rather than peripheral. This distinguishes it from all other pharmacological approaches to sexual dysfunction, which target either peripheral vascular tone (PDE5 inhibitors such as sildenafil) or systemic hormone levels (testosterone, estrogen). The molecule is small enough and sufficiently lipophilic to cross the blood-brain barrier in meaningful quantities after subcutaneous injection.

The MC4R activation pathway increases dopaminergic and oxytocin neurotransmission in circuits that mediate sexual interest and motivated behavior. Critically, the mechanism operates independently of sex hormone levels, which is clinically relevant for premenopausal women with HSDD in whom gonadal hormone concentrations may be within the normal range.

What the Research Shows

The pivotal evidence supporting the FDA approval of Vyleesi came from the RECONNECT trials — two identical phase 3, randomized, double-blind, placebo-controlled studies in premenopausal women with acquired, generalized HSDD. In both trials, bremelanotide 1.75 mg SC demonstrated statistically significant improvements over placebo on the co-primary endpoints: the Female Sexual Function Index – Desire domain (FSFI-D) score and the Female Sexual Distress Scale – Desire/Arousal/Orgasm (FSDS-DAO) item 13 score. These results supported the June 2019 FDA approval.

Earlier-phase clinical work explored bremelanotide in both men (for erectile dysfunction) and women using intranasal and subcutaneous delivery routes. The intranasal program was discontinued due to transient hypertensive episodes in some subjects; the subcutaneous formulation in the Vyleesi autoinjector produces more predictable absorption with a better cardiovascular safety profile, though transient blood pressure elevations remain a labelled risk and the compound is contraindicated in patients with cardiovascular disease.

Pharmacokinetics

According to the Vyleesi prescribing information (FDA, 2019), the mean terminal half-life of bremelanotide is approximately 2.7 hours (range 1.9–4.0 hours) after subcutaneous injection. Maximum plasma concentration (Cmax) is reached within approximately 1 hour. The compound is metabolized primarily by hydrolysis. At the approved 1.75 mg SC dose, transient increases in blood pressure (mean peak increase approximately 6 mmHg systolic, 3 mmHg diastolic) are observed within 4 hours of administration. Blood pressure returns to near-baseline within 12 hours for most patients.

Common Research Dose Ranges

Not medical advice. These are ranges reported in research literature, not personalized recommendations. Consult your physician.

The FDA-approved label specifies a single 1.75 mg subcutaneous dose administered at least 45 minutes before anticipated sexual activity, no more than once in 24 hours (Vyleesi Prescribing Information, FDA, 2019). This is the only dose supported by phase 3 human trial data. Literature reports for research-use contexts reference the same 1.75 mg SC dose as the established pharmacologically active level.

Storage

The Vyleesi autoinjector is stored at room temperature, not exceeding 30 °C. Lyophilized research-grade bremelanotide powder should be stored at −20 °C; once reconstituted with bacteriostatic water, the solution should be kept at 2–8 °C and used within 28 days.

What PT-141 / Bremelanotide Is NOT

PT-141 / bremelanotide is not Melanotan II. Melanotan II is a non-selective cyclic heptapeptide that agonizes MC1R, MC3R, MC4R, and MC5R simultaneously — producing potent tanning (MC1R), sexual effects (MC4R), and appetite suppression, alongside significant off-target adverse effects. Bremelanotide was engineered specifically to reduce MC1R activity and eliminate the tanning effect while retaining MC3R/MC4R agonism. The two compounds have overlapping structural ancestry but substantially different receptor selectivity profiles and safety data. PT-141 also should not be confused with flibanserin (Addyi), the other FDA-approved HSDD treatment, which is a serotonin-norepinephrine modulator, not a melanocortin agonist, and requires daily oral dosing.

References

Citations for this guide are listed below. All links resolve to the official source document.