PT-141

PT-141, also known as bremelanotide, is a synthetic cyclic heptapeptide that acts as a non-selective agonist at melanocortin receptors, specifically MC1R, MC3R, and MC4R. It was derived from Melanotan II (MT-II), an alpha-MSH analog originally developed for skin tanning, when researchers noticed unexpected sexual arousal as a pronounced side effect in early clinical trials. PT-141 was subsequently developed as a dedicated sexual dysfunction therapeutic, representing a fundamentally new class of treatment.

The mechanism of PT-141 is categorically different from PDE5 inhibitors (sildenafil/Viagra, tadalafil/Cialis). Those drugs work peripherally, they increase blood flow to genital tissue and require existing arousal to produce an effect. PT-141 acts centrally in the brain, activating MC3R and MC4R receptors in the hypothalamus and limbic system, which upregulate dopaminergic signaling pathways involved in sexual motivation and desire. PT-141 addresses desire and motivation directly, not just the physical response, making it effective in both men and women, including those who do not respond to PDE5 inhibitors.

In 2019, the FDA approved bremelanotide (brand name Vyleesi) for hypoactive sexual desire disorder (HSDD) in premenopausal women, the first centrally-acting pharmacological treatment for HSDD ever approved. The approved form is a subcutaneous autoinjector at 1.75 mg per dose, used as needed before anticipated sexual activity. Clinical trials demonstrated statistically significant improvements in sexual desire and reductions in distress related to low libido, making PT-141 one of the few peptides to complete the full FDA approval pathway.

For research use, PT-141 is commonly reconstituted from a 10 mg lyophilized vial. Adding 5 mL of bacteriostatic water gives a concentration of 2 mg/mL. A standard 1 mg dose draws 0.5 mL, 50 units on a U-100 syringe. Administer subcutaneously in the abdomen approximately 45–60 minutes before anticipated sexual activity. Effects typically onset within 45–60 minutes, peak around 2 hours, and can persist for 6–12 hours. Unlike PDE5 inhibitors, PT-141 does not require simultaneous sexual stimulation to initiate its central effects.

The most common side effects are transient nausea (first 30–90 minutes post-injection), flushing, and mild to moderate increases in blood pressure. Blood pressure elevation is the primary safety concern, PT-141 is contraindicated in individuals with cardiovascular disease, uncontrolled hypertension, or those taking antihypertensive medications. The Vyleesi prescribing information includes a black-box style warning against use with cardiovascular disease. Starting at 1 mg rather than 1.75 mg significantly reduces nausea and blood pressure effects in most individuals.