PT-141 Nasal Spray

PT-141 is the research name of bremelanotide, a synthetic cyclic peptide of seven amino acids. It belongs to the melanotan family: chemically it is what Melanotan II becomes when the terminal amide is turned into a free acid. PT-141 still acts on the pigment receptors, but it was developed specifically for the central effects on desire and arousal and is taken occasionally rather than daily. In the US, bremelanotide has been approved since 2019 as an on-demand autoinjector for premenopausal women with low sexual desire (brand name Vyleesi). That makes it one of the few peptides in this lexicon that went through a complete clinical programme all the way to approval (Mayer 2020).

This variant is the finished nasal spray: 10mg of PT-141 dissolved in 5ml of saline plus 0.4ml of bacteriostatic water, 5.4ml in total, so 1.85mg per millilitre. One spray delivers 0.1ml and contains about 185mcg (0.19mg) of peptide. On paper that is 54 sprays per bottle, about 50 remain usable after priming the pump. Nothing to mix and no syringe. The spray is prepared fresh from a vial after you order and ships as an express item. If you want the subcutaneous form at study doses, the PT-141 vial is still there and has its own lexicon entry.

One thing to get straight from the start: nasal PT-141 was genuinely tested in humans in the early 2000s, but at 7 to 20mg per use. This bottle delivers 0.19 to 0.74mg with 1 to 4 sprays, a fraction of that. It is a low-dose format, not a stand-in for the injection.

This information is for research and educational purposes only. No medical advice.

PT-141 activates several melanocortin receptors without being selective for one. According to the prescribing information for the injection, two matter most at usual doses: the melanocortin-4 receptor (MC4R) in the brain and MC1R on pigment cells, with MC3R playing a weaker part. For desire and arousal MC4R is the key one; it sits in brain regions that govern these processes, above all the hypothalamus. In animal models, activation there triggers a release of dopamine that acts as the starting signal for sexual interest. As far as is understood today, the effect is therefore central and starts with the drive rather than with the blood vessels. How exactly desire rises is, according to the prescribing information, not yet known. PDE-5 inhibitors work the other way round. They act peripherally via blood flow and need existing arousal; in trials PT-141 produced erections even without visual stimulation (Diamond 2004).

Because melanocortin receptors are spread across the whole body, the same mechanism explains the side effects: MC1R on pigment cells accounts for the hyperpigmentation seen with too-frequent dosing, central MC4R activation for the nausea. A pull on the circulation shows up as a brief rise in blood pressure with a simultaneously slower pulse (White 2017). Unlike Melanotan II, tanning is not the goal with PT-141 and stayed rare at the occasional dosing used in the approval trials (Clayton 2022).

At a little over 1,000 daltons, PT-141 is a small, water-soluble peptide that crosses the richly perfused nasal lining straight into the bloodstream, bypassing the stomach and liver. For PT-141 this was actually measured, which makes it one of the few peptides with real nasal human data: in the phase 1 study in healthy men, peak levels and total exposure rose with the nasal dose, the peak arrived at a median of 30 minutes and the half-life was about 2 hours. The first erection also came after roughly 30 minutes (Diamond 2004). So the spray acts fast and is gone again within a few hours.

The catch is the amount. In the same study a statistically significant effect only appeared above 7mg nasally. In women single nasal doses of 20mg were tested (Diamond 2006). Subcutaneously, 1.75mg is enough to be the approved dose (Mayer 2020). According to the prescribing information for the injection, 20mg nasally reaches only about 2.5 times the peak level of 1.75mg subcutaneously, from more than eleven times the amount. So only part of a nasal dose reaches the blood, the rest is probably broken down by peptidases in the mucosa or drains with the secretions into the throat. With this bottle, 7mg would be about 38 sprays, three quarters of the contents in one go. 20mg would be more than the whole bottle. What was ultimately developed and approved was the subcutaneous form.

For practice this means: with 1 to 4 sprays you stay well below the systemic exposure that worked in the trials. That makes the spray the gentler option as far as nausea and blood pressure go, but also the weaker one. Anyone after a reliable effect at study strength belongs with the vial, not with ever more sprays.

The nasal form of PT-141 has a short but real study history. In the double-blind, placebo-controlled phase 1 work in healthy men and in men with mild to moderate erectile dysfunction (Diamond 2004), PT-141 was given as a nasal spray in rising doses and erections were measured with RigiScan. Above 7mg the erectile response was significant versus placebo, in healthy men even without visual stimulation. No maximum tolerated dose was reached. The most common adverse events were flushing and nausea. Vital signs, laboratory values and ECGs showed no clinically relevant change.

In 18 premenopausal women with arousal disorder, a single nasal dose of 20mg was tested in a crossover against placebo (Diamond 2006). More women reported moderate to high desire after PT-141 (p = 0.011). Among those who attempted intercourse within 24 hours, significantly more were satisfied with their level of arousal. Objectively measured vaginal blood flow, on the other hand, did not change. That fits the central mechanism: desire moves, the vessels do not.

Development then continued with the subcutaneous form. Two identical phase 3 trials with 1.75mg on demand in a total of 1,267 women showed, over 24 weeks, a significant increase in desire and less distress versus placebo. US approval followed in 2019 (RECONNECT trials, summarised in Mayer 2020). The entire development programme covers around 3,500 subjects in 43 studies (Clayton 2022). For carrying this over to the spray: efficacy is established for the injection at study strength, for nasal doses below 1mg there are no data.

The evidence comes almost entirely from the subcutaneous programme at 1.75mg. There, nausea was by far the most common: 40 percent on bremelanotide against 1.3 percent on placebo, followed by flushing (20 percent) and headache (11 percent) (Clayton 2022). According to the prescribing information, nausea usually began within the first hour, lasted about 2 hours and showed up mainly after the first dose (21 percent, around 3 percent with later doses). It was the most common reason for stopping (Clayton 2022). At 0.19 to 0.74mg nasally the systemic dose is far lower, but in the nasal phase 1 study flushing and nausea occurred just the same at the high doses tested there (Diamond 2004). Starting low is therefore not a ritual, it is how you dodge the nausea.

Blood pressure: bremelanotide raises blood pressure briefly. Under 24-hour ambulatory monitoring, systolic pressure in the first 4 hours after 1.25 to 1.75mg sat 2.4 to 3.2 mmHg above placebo, the peaks mostly lasted under 15 minutes. The pulse dropped by just under 5 beats at the same time (White 2017). Small, but measurable. Anyone with high or untreated blood pressure or a cardiovascular risk leaves PT-141 alone in any form. The prescribing information for the injection rules out uncontrolled hypertension and known cardiovascular disease. The review of the development programme advises caution with cardiovascular risk (Clayton 2022).

Pigment: as a melanocortin agonist, PT-141 can darken skin, moles and freckles, mostly on the face and in darker skin types. Used by the label rule this was rare, after up to 16 daily doses it affected more than a third (Clayton 2022). According to the prescribing information the patches did not clear in everyone after stopping. Hence the limit of 8 uses per month. Specific to the nasal route are irritation of the lining, sneezing, a runny nose and a bitter taste in the throat when solution runs backwards. With a blocked nose the spray achieves little.

The spray belongs in the fridge at 2 to 8 degrees, protected from light in its outer packaging. Keep it upright so the dip tube stays in the solution. Do not freeze it and keep it out of the door compartment, where the temperature swings every time it opens. A few hours at room temperature in the post or in a bag do no harm; the approved finished product is even allowed to sit at room temperature up to 25 degrees permanently. Even so, the bottle should not stand warm or in the sun for long.

Once opened, the solution keeps for several months in the fridge. PT-141 is a cyclic peptide closed by a lactam bridge, with no free cysteines, which makes it considerably more stable than many linear peptides. Only 0.4ml of the 5.4ml is bacteriostatic water, so its preservative is heavily diluted and protects the solution only to a limited degree. That is why hygiene counts: wipe the nozzle with a clean tissue after each use, put the cap back on and do not share the bottle. If the solution turns gel-like, lumpy or smells different, stop using it. Slight cloudiness on its own is not a reason.

For the arithmetic: on paper the bottle holds 54 sprays, about 50 remain after priming the pump. At 2 sprays per use and at most 8 uses a month they last about three months; at 4 sprays, around six weeks. That lines up with the shelf life after opening.