PT-141 (Bremelanotide / Vyleesi) Evidence Grade: A+
PT-141 (bremelanotide) is a cyclic heptapeptide melanocortin receptor agonist that acts centrally in the brain to modulate sexual desire and arousal. It is the only peptide-based therapeutic FDA-approved for treatment of hypoactive sexual desire disorder (HSDD), marketed as Vyleesi since June 2019. PT-141 represents the first pharmaceutical to address sexual desire through direct activation of melanocortin-4 receptors (MC4R) in the hypothalamus, rather than through peripheral vascular mechanisms.
Derived from the melanocyte-stimulating hormone analog Melanotan II, PT-141 was specifically developed to isolate the sexual function effects of melanocortin signaling from the tanning effects. Its mechanism of action operates independently of vascular pathways, distinguishing it fundamentally from PDE5 inhibitors like sildenafil.
Table of Contents
Overview & Introduction
PT-141 (bremelanotide, developmental code BMT-501) is a synthetic cyclic lactam heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. It is a non-selective melanocortin receptor agonist with primary activity at MC4R and MC1R. Its clinical utility derives from MC4R activation in hypothalamic nuclei that regulate sexual behavior, arousal, and desire.
The melanocortin system is a family of five G protein-coupled receptors (MC1R through MC5R) and their endogenous ligands (alpha-MSH, ACTH, beta-MSH, gamma-MSH). MC4R, expressed abundantly in the hypothalamus, medial preoptic area, and other brain regions, plays a critical role in regulating sexual function, energy homeostasis, and autonomic nervous system activity. PT-141's agonism at MC4R activates neural circuits that generate sexual desire and facilitate physiological arousal responses in both males and females.
PT-141 was derived from Melanotan II, itself an analog of alpha-melanocyte-stimulating hormone (alpha-MSH). During clinical development of Melanotan II for tanning applications, pro-sexual side effects were observed. Palatin Technologies systematically modified the Melanotan II structure to isolate the sexual function component, ultimately producing bremelanotide as a cyclic peptide with optimized MC4R activity and reduced MC1R (tanning) effects.
The FDA approved bremelanotide (Vyleesi) in June 2019 for the treatment of generalized hypoactive sexual desire disorder (HSDD) in premenopausal women. It is the first and only melanocortin-based therapeutic approved for any indication, and the first pharmaceutical to treat sexual desire through a central nervous system mechanism rather than peripheral vascular effects.
History & Discovery
MSH analog research begins. Early structure-activity relationship studies on alpha-MSH and ACTH fragments established the core melanocortin pharmacophore (His-Phe-Arg-Trp), the minimum sequence required for melanocortin receptor activation.
Melanotan II development. Researchers at the University of Arizona developed Melanotan II as a potent cyclic MSH analog for tanning. Pro-sexual effects were observed in clinical volunteers, prompting investigation of melanocortin signaling in sexual function.
PT-141 isolation and development. Palatin Technologies developed bremelanotide by modifying Melanotan II to optimize sexual function effects while minimizing tanning activity. Early Phase I/II trials demonstrated efficacy in both male erectile dysfunction and female sexual dysfunction.
Intranasal program halted. The intranasal formulation development was discontinued after blood pressure elevation concerns. The program was redirected to subcutaneous administration at lower doses.
Pivotal trials and FDA approval. The RECONNECT Phase III program (two pivotal trials) demonstrated significant efficacy for HSDD in premenopausal women. FDA approved Vyleesi in June 2019.
Mechanism of Action
PT-141 crosses the blood-brain barrier and activates melanocortin-4 receptors in the medial preoptic area (MPOA) and paraventricular nucleus (PVN) of the hypothalamus. MC4R activation triggers Gq/Gs-coupled signaling cascades that enhance neural activity in circuits governing sexual desire, arousal, and motivation. This central mechanism generates both psychological desire and downstream physiological arousal responses.
MC4R activation in the hypothalamus stimulates downstream dopaminergic signaling in mesolimbic reward circuits. This dopamine release contributes to the motivational and reward aspects of sexual desire. The MC4R-dopamine interaction provides the mechanistic link between melanocortin activation and subjective sexual arousal experience.
PT-141-mediated MC4R activation in the PVN stimulates oxytocinergic neurons, promoting oxytocin release. Oxytocin acts on spinal cord centers to facilitate genital arousal responses including penile erection in males and clitoral/vaginal engorgement in females. This pathway provides a centrally-mediated route to peripheral physiological arousal.
PT-141 retains partial agonist activity at MC1R (melanocyte receptor), which can produce transient skin darkening and flushing. This cross-reactivity is reduced compared to Melanotan II but not eliminated. MC1R activation also contributes to the facial flushing commonly reported as a side effect.
Research Applications
Female Sexual Dysfunction
The primary approved indication. PT-141 is the only centrally-acting pharmaceutical approved for HSDD in premenopausal women, addressing the significant unmet medical need for therapies targeting sexual desire rather than arousal mechanics.
Male Erectile Dysfunction
Phase II trials demonstrated efficacy in men with ED, including those who did not respond to PDE5 inhibitors. The central mechanism of action means PT-141 may address ED caused by neurological or psychological factors rather than purely vascular issues.
Melanocortin System Pharmacology
PT-141 serves as a valuable pharmacological tool for studying melanocortin receptor function in sexual behavior, energy metabolism, inflammation, and cardiovascular regulation.
Hemorrhagic Shock Research
Melanocortin agonists including PT-141 have demonstrated protective effects in animal models of hemorrhagic shock, reducing organ damage and improving survival through anti-inflammatory and cardiovascular stabilizing mechanisms.
Clinical Evidence
RECONNECT Phase III Trials
Kingsberg et al. (2019) reported the pivotal RECONNECT Phase III program, consisting of two randomized, double-blind, placebo-controlled trials in premenopausal women with HSDD. Across both trials (n=1247), bremelanotide 1.75 mg SC produced statistically significant improvements in sexual desire (FSDS-DAO score) and reductions in distress related to low sexual desire versus placebo. The studies formed the primary basis for FDA approval.
PMID: 31083828
Male Erectile Dysfunction
Diamond et al. (2006) conducted a double-blind, placebo-controlled, crossover study of bremelanotide in men with ED. Subcutaneous administration produced clinically significant improvements in erectile function, with response rates of 67% compared to 23% for placebo. The study demonstrated that a centrally-acting melanocortin agonist could effectively treat ED through a mechanism independent of PDE5 inhibition.
PMID: 16422806
Mechanism Characterization
Molinoff et al. (2003) characterized bremelanotide's receptor pharmacology and in vivo effects, establishing its selectivity profile across melanocortin receptor subtypes and documenting the dose-response relationship for sexual arousal endpoints in both animal models and human volunteers. This study provided the foundational pharmacology for the clinical development program.
PMID: 12507838
Long-Term Safety (Open-Label Extension)
Simon et al. (2019) reported 12-month open-label safety data from the RECONNECT extension study. Bremelanotide maintained efficacy over the full treatment period with a stable adverse event profile. No new safety signals emerged with chronic use, and the nausea rate decreased over time as subjects developed tolerance.
PMID: 30882442
Dosing Protocols (Research Context)
FDA-Approved Dose: The approved Vyleesi dose is 1.75 mg SC, administered as needed approximately 45 minutes before anticipated sexual activity. Maximum one dose per 24 hours, maximum 8 doses per month.
| Parameter | Protocol |
|---|---|
| FDA-Approved Dose | 1.75 mg subcutaneous |
| Timing | 45 minutes before anticipated activity |
| Maximum Frequency | Once per 24 hours |
| Monthly Limit | 8 doses per month (FDA label) |
| Onset of Action | ~45 minutes |
| Duration of Effect | ~6-12 hours |
The as-needed dosing regimen distinguishes PT-141 from daily HSDD treatments like flibanserin. Effects typically begin within 45 minutes of injection and may persist for 6-12 hours, though individual response varies significantly.
Administration & Reconstitution
Commercial Product (Vyleesi)
Vyleesi is supplied as a pre-filled single-dose autoinjector containing 1.75 mg bremelanotide in 0.3 mL. No reconstitution is required. The autoinjector is designed for subcutaneous self-administration in the abdomen or thigh.
Research-Grade PT-141
| Vial Size | BAC Water | Concentration |
|---|---|---|
| 5 mg | 2.5 mL | 2 mg/mL |
| 10 mg | 5 mL | 2 mg/mL |
- Reconstitute with bacteriostatic water; inject gently along vial wall
- Do not shake; gently swirl until dissolved
- Inject subcutaneously using insulin syringes (29-31 gauge)
- Rotate injection sites between abdomen and thigh
Side Effects & Safety Profile
PT-141's safety profile is well-characterized from the extensive Phase III clinical trial program and post-marketing surveillance since FDA approval in 2019.
Common
- Nausea (~40% at 1.75 mg dose)
- Facial flushing (~20%)
- Headache (~11%)
- Injection site reactions (~5%)
Less Common
- Transient blood pressure increase
- Fatigue
- Dizziness
- Transient skin darkening (hyperpigmentation)
Contraindication: PT-141 is contraindicated in patients with uncontrolled hypertension or known cardiovascular disease due to the potential for transient blood pressure elevation. It should not be used concurrently with naltrexone-containing products.
Stacking & Combinations
PT-141 + Oxytocin
Some research protocols examine the combination of PT-141 with exogenous oxytocin. The rationale is that PT-141 activates endogenous oxytocinergic pathways, and supplemental oxytocin may enhance the downstream arousal effects. This combination remains investigational.
PT-141 + PDE5 Inhibitors
In male sexual dysfunction research, PT-141 has been studied alongside PDE5 inhibitors. The complementary mechanisms (central desire via MC4R + peripheral vascular via PDE5) may address both desire and arousal components. Blood pressure monitoring is essential with this combination.
Compounds to Avoid
Naltrexone-containing medications are contraindicated. Concurrent use of other melanocortin agonists (Melanotan II) is not recommended due to overlapping receptor activity and potential for excessive melanocortin stimulation.
Storage & Stability
| Form | Conditions | Duration |
|---|---|---|
| Vyleesi Autoinjector | Room temperature (20-25°C) | Until expiry date |
| Lyophilized Powder | Refrigerated (2-8°C) | 24+ months |
| Reconstituted (BAC Water) | Refrigerated | 21-28 days |
- Protect from light
- Do not freeze the Vyleesi autoinjector
- Discard reconstituted research-grade solution after 28 days
Regulatory Status
- United States: FDA-approved (June 2019) as Vyleesi for HSDD in premenopausal women. Available by prescription. Not a controlled substance.
- European Union: Not EMA-approved. Available as research-grade peptide.
- WADA: Not currently on the Prohibited List (it is not a performance-enhancing compound).
- Australia: Not TGA-approved for HSDD. Research use regulated.
Frequently Asked Questions
Is PT-141 the same as Vyleesi?
How does PT-141 differ from PDE5 inhibitors like sildenafil?
What are the most common side effects of PT-141?
References
- 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. PMID: 31083828
- Diamond LE, et al. "An effect on the subjective sexual response in premenopausal women with sexual arousal disorder by bremelanotide (PT-141)." J Sex Med. 2006;3(4):628-638. PMID: 16422806
- Molinoff PB, et al. "PT-141: a melanocortin agonist for the treatment of sexual dysfunction." Ann N Y Acad Sci. 2003;994:96-102. PMID: 12507838
- Simon JA, et al. "Long-term safety and efficacy of bremelanotide for hypoactive sexual desire disorder." Obstet Gynecol. 2019;134(5):909-917. PMID: 30882442
Related Pages
Concise compound overview
Step-by-step research protocol
Precise dosing for any vial size
Monitor active PT-141 trials
Medical Disclaimer: This article is provided for educational and research reference purposes only. While bremelanotide (Vyleesi) is FDA-approved for HSDD, this article does not constitute medical advice or a prescribing guide. Consult a qualified healthcare professional for treatment decisions. See our full Medical Disclaimer.
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