The short version

Plain English first. Everything below this section is the same material with the sources, the numbers and the caveats attached.

What PT-141 is

PT-141 is bremelanotide: a seven amino acid ring, closed by a bridge between an aspartate and a lysine side chain. It came out of a University of Arizona programme that was trying to build a tanning peptide, and found something else instead.

The formula line is quoted from the FDA label itself, which is a better source than any supplier catalogue.

It is Melanotan II with one atom changed

The two molecules are the same ring in the same order. The difference is the very end:

That one substitution is why one of them tans you reliably and the other is a licensed medicine. Bremelanotide is reported to be an active metabolite of Melanotan II — the citation is Hadley 2005, which we could not open, so we state the structural difference as fact and the metabolite relationship as a report.

Vendors routinely print the free-base CAS beside acetate product and quote 1,025 Da for material that is salt. Ask which form, and ask what the milligram figure counts.

How it works

This is one of the few compounds here where the mechanism is genuinely established rather than asserted. It is a melanocortin agonist acting centrally, at MC3 and MC4 receptors.

Molinoff and colleagues, 2003: PT-141 "is an agonist at melanocortin receptors including the MC3R and MC4R, which are expressed primarily in the central nervous system." Systemic dosing lights up hypothalamic neurons. MC4R is understood to modulate sexual desire. None of that is contested.

"It works on the brain, not the blood vessels"

You will see this everywhere, usually as the reason PT-141 is supposedly safer or cleaner than a PDE5 inhibitor. It is directionally true and routinely overstated.

The accurate statement is that PT-141 is centrally initiated and systemically active. It is a different starting point, not an absence of effect on the rest of you.

The pigmentation is the same mechanism

Bremelanotide is not selective. MC1R — the pigmentation receptor — is part of the family it agonises. That is not a side effect bolted on from somewhere else; it is the same pharmacology doing something you did not ask for. See the safety section, where the numbers are worse than most people expect.

Pharmacokinetics

Every figure in this section comes from an approved drug label. Nothing else in this library can say that.

Two numbers worth pausing on

Bioavailability of roughly 100% under the skin. Unusual for a peptide, and it is precisely why the subcutaneous route succeeded where the nasal route failed. Intranasal needed more than 7 mg to produce any erectile signal. Subcutaneous does the job at 1.75 mg.

A 2.7 hour half-life, against a blood pressure effect that peaks at 2 to 4 hours and takes up to 12 hours to settle. The cardiovascular effect outlasts the drug.

What the evidence shows

Two phase 3 trials, 1,267 patients, double-blind, placebo-controlled, published in Obstetrics & Gynecology, reviewed by the FDA and approved. Then read what they found.

The RECONNECT trials

Two identical 24-week trials in premenopausal women with hypoactive sexual desire disorder. The two co-primary endpoints were a desire score running 1.2 to 6.0, and a distress question scored 0 to 4.

Statistically significant, all four. The difference from placebo is about 0.3 to 0.4 points on a 4.8-point scale — and the standard deviations run 1.0 to 1.2, three times the size of the effect.

The re-analysis

Spielmans, 2021, in the Journal of Sex Research, went back through the trial protocols. The findings are uncomfortable:

• 72.7% of the outcomes listed in the protocols were not reported as specified. Fifteen measures that were not in the protocols were reported instead.
• Satisfying sexual events were demoted from co-primary to secondary more than a year after the trials began, and the published paper did not disclose the change.
• Dropping out because of side effects: 18.5% on the drug against 0.9 to 3.0% on placebo — and the original paper did not report it.
• Of those who finished and were offered a year's free continuation, 40.5% on the drug took it, against 69.4% on placebo. People who had been on the real thing were markedly less keen to carry on than people who had been on nothing.
• 35% of women who met the sponsor's own definition of a responder said in exit interviews that they had experienced no meaningful benefit.

In fairness: a published commentary disputes this re-analysis (PMID 33835907). We could not open it, so we are not characterising its arguments — only telling you it exists.

The evidence in men, which is the way it is actually sold

Everything above is in women. The approved label says, verbatim, that the drug "is not indicated for the treatment of HSDD in postmenopausal women or in men" and "is not indicated to enhance sexual performance." Here is the entire male evidence base:

Reconstitution

Unusually, there is a correct answer here: 1.75 mg, because that is the licensed dose, and it is the only dose in this compound's history with a completed efficacy trial behind it.

Two millilitres is the sensible choice. It puts a full dose inside a third of a syringe and keeps every draw on a round-ish number.

On solubility, our two best supplier sources disagree by an order of magnitude — one says 5 mg/mL in buffered saline, another says over 50 mg/mL in water. Neither publishes a method. At the concentrations above it dissolves either way, so the disagreement is academic here, but it is worth knowing that neither figure is trial-derived.

Reported protocols

The approved regimen is specific, and everything sold departs from it in at least one direction. Here it is, verbatim from the label.

What circulates, and where each number comes from

Why the monthly cap is the number to respect

It is easy to read "8 doses per month" as a conservative dosing convention. It is not. It does not appear in the dosage section of the label at all. It sits inside the warning about skin pigmentation, immediately after this:

A 16-week daily protocol is roughly 112 consecutive doses. The label's own data describes what happens well before you get there. That the cap sits inside the pigmentation warning rather than the dosing instructions is our reading of the label's structure — we could not find FDA stating the rationale in so many words — but the placement is not ambiguous.

One further claim we chased and could not find: that daily 2.5 mg protocols "have been studied in obese women." No such study exists that we could locate.

Storage

Lyophilised, sealed, cold, dark and dry. Our storage guide covers the general conventions.

Supplier guidance for research powder is −20 °C for a year, −80 °C for two, and once in solvent, a month at −20 °C. These are supplier stability claims rather than stability-indicating data.

Reported effects

This is the best-documented safety section in this library, and it is not reassuring. Everything below is from the approved label, describing 627 people on the drug against 620 on placebo.

The label, verbatim: "The discontinuation rate due to adverse reactions was 18% among patients treated with VYLEESI and 2% among patients treated with placebo." Nausea alone required anti-emetics in 13% of patients, and pre-treating with ondansetron did not help.

"Well tolerated" is the single most common thing said about this compound online. Forty per cent nausea and an 18% dropout rate is not what that phrase means.

Blood pressure — the two contraindications

FDA's own risk review quotes a smaller figure, 2 to 3 mmHg. The two are almost certainly different quantities — a maximum observed against a mean adjusted for placebo — but we found nothing reconciling them, so we quote the label, which is the regulated text.

Skin pigmentation, and why it is not a tan

At label frequency, focal hyperpigmentation — face, gums and breasts — occurred in 1% of patients and in none on placebo. With daily dosing it reached 38% in eight days.

Two things the label is explicit about, and both matter:

• "Patients with dark skin were more likely to develop focal hyperpigmentation." FDA's review puts numbers on it: 4.1% in Black patients against 0.6% in white patients.
• "Resolution of the focal hyperpigmentation was not confirmed in all patients after discontinuation." FDA's review is blunter — only about half resolved. It may be permanent.

This is why "PT-141 doesn't cause tanning" is wrong as usually stated. The honest version is that it produces far less pigmentation than Melanotan II at licensed frequency, and that what it does produce is blotchy, focal, on the face, and possibly permanent. That is not a tan. It is a documented adverse reaction.

Interactions and liver

The drug slows gastric emptying, so it can blunt oral medicines that need a threshold concentration — antibiotics, for instance. The label singles out oral naltrexone, warning of "the severe consequence of naltrexone treatment failure." NIH's LiverTox rates it a possible rare cause of liver injury on a single reported case.

Regulatory status

PT-141 sits differently from everything else in this library, in three separate ways — and each one is counterintuitive enough to be worth the explanation.

United States — it is an approved drug

Approved 21 June 2019 as Vyleesi, NDA 210557, for premenopausal women with acquired, generalised HSDD. Sold to Cosette Pharmaceuticals in January 2024 and still marketed.

That approval also explains why bremelanotide was not among the seven peptides before FDA's compounding committee in July 2026. The statute sets out three routes for a substance used in compounding, and the second is being a component of an approved drug. Bremelanotide is exactly that, so it never needs the bulks list at all. BPC-157, TB-500, Epitalon and the rest are on that track precisely because no approved drug contains them.

None of which makes a research vial lawful. Compounding rules govern a licensed pharmacist preparing a medicine for an identified patient from registered material. They have nothing to say about a vial sold for laboratory use.

Canada — not named, which is not the same as permitted

Health Canada's advisory of 9 April 2026 names fourteen peptides. We read it in full. Neither "PT-141" nor "bremelanotide" appears anywhere in it — while Melanotan I and II do. Two nearly identical molecules, one named and one not.

Sport — the one compound here that S0 does not catch

We searched the 2026 Prohibited List for "bremelanotide", "PT-141", "melanotan" and "melanocortin". None appears.

For every other compound in this library that is where the analysis begins, not ends, because Section S0 sweeps up anything "with no current approval by any governmental regulatory health authority for human therapeutic use." Bremelanotide has current FDA approval. On the plain text of S0, it falls outside it — and it is not a peptide hormone or growth factor under S2 either.

Three caveats an athlete must not skip. This is our reading of the List's text, not a WADA ruling — we found no decision or guidance addressing bremelanotide. S0 explicitly covers discontinued drugs, so if Vyleesi ever left the market the status would arguably flip. And national anti-doping bodies can be stricter than WADA. Ask your own organisation.

Sentient Biogenix supplies PT-141 for laboratory research use only. It is not for human or veterinary use.

Questions we actually get

Does it work for men?

Nobody has published a completed, placebo-controlled trial of subcutaneous PT-141 with an efficacy endpoint in men. The approved label says in as many words that the drug is not indicated in men and not indicated to enhance sexual performance. The male evidence that exists is intranasal, from 2004 and 2005, at four times the dose, by a route the FDA halted — plus one paper the journal has since flagged with an Expression of Concern.

How well does it work in women, then?

On a desire scale running 1.2 to 6.0, it moved scores about 0.3 to 0.4 points more than placebo. The number of actual satisfying sexual encounters did not change at all. When women who had finished the trial were offered a free year of continued treatment, more of the placebo group signed up than the drug group.

Is 2 mg the standard dose?

No. 1.75 mg is the licensed dose. The 2 mg figure has no citation anywhere we could find; it appears to be the approved regimen with the number rounded up and the population swapped.

Will it tan me, or stain me?

Neither, reliably, but the risk is real. One per cent of patients at licensed frequency developed blotchy pigment on the face, gums or breasts. Dosed daily for eight days, 38% did. It is more likely on darker skin, and about half the cases in FDA's review never resolved.

Why only eight doses a month?

Because of the pigmentation. That limit is not in the dosing section of the label — it sits inside the warning about skin discolouration, right after the 38% figure. Protocols recommending daily use are running straight at the thing the cap exists to prevent.

Is it safe for me if I have high blood pressure?

The label contraindicates it in uncontrolled hypertension and in known cardiovascular disease. Those are the only two contraindications on it, and they exist because the drug reliably raises blood pressure for several hours after every dose. This is not a compound to take without knowing your numbers.

Why isn't it banned in sport when everything else here is?

Because it is an approved medicine. The catch-all that captures the rest of this library only applies to substances with no approval anywhere. Melanotan II — almost the same molecule — is caught, because nobody has ever licensed it. Do not take that as clearance from us; ask your own anti-doping body.

References

1. US Food and Drug Administration. VYLEESI (bremelanotide injection) prescribing information, NDA 210557, revised 03/2024. dailymed.nlm.nih.gov — the structure and molecular weight, the indication and its limitations, the dose and frequency, all pharmacokinetics, the adverse reaction table, the blood pressure and hyperpigmentation warnings, the contraindications, and the storage condition.
2. US Food and Drug Administration. VYLEESI label PDF, 210557s002, 2020. accessdata.fda.gov
3. US Food and Drug Administration. Risk assessment review, 210557Orig1s000. accessdata.fda.gov — hyperpigmentation by skin colour, and the proportion that resolved.
4. Kingsberg SA, Clayton AH, Portman D, et al. Bremelanotide for the treatment of hypoactive sexual desire disorder: two randomized phase 3 trials. Obstetrics & Gynecology 2019;134(5):899–908. PMID 31599840. pubmed.ncbi.nlm.nih.gov
5. Spielmans GI. Re-analyzing phase III bremelanotide trials for "hypoactive sexual desire disorder" in women. The Journal of Sex Research 2021. DOI 10.1080/00224499.2021.1885601. taylorandfrancisgroup.com — the unreported outcomes, the endpoint switch, the dropout rate and the extension uptake. A published commentary disputes this analysis (PMID 33835907); we could not read it.
6. Simon JA, Kingsberg SA, Portman D, et al. Long-term safety and efficacy of bremelanotide for hypoactive sexual desire disorder. Obstetrics & Gynecology 2019;134(5):909–917. PMID 31599847. pubmed.ncbi.nlm.nih.gov
7. Molinoff PB, Shadiack AM, Earle D, Diamond LE, Quon CY. PT-141: a melanocortin agonist for the treatment of sexual dysfunction. Annals of the New York Academy of Sciences 2003;994:96–102. PMID 12851303. pubmed.ncbi.nlm.nih.gov
8. Diamond LE, Earle DC, Rosen RC, Willett MS, Molinoff PB. Double-blind, placebo-controlled evaluation of the safety, pharmacokinetic properties and pharmacodynamic effects of intranasal PT-141. International Journal of Impotence Research 2004;16(1):51–59. PMID 14963471. pubmed.ncbi.nlm.nih.gov — the source of the "above 7 mg intranasal" figure.
9. Palatin Technologies / King Pharmaceuticals. Announcement of delayed phase 3 plans for bremelanotide, 30 August 2007, filed with the SEC. sec.gov — FDA's "serious concerns about the acceptable benefit/risk ratio", citing blood pressure as its greatest safety concern.
10. Expression of Concern: Salvage of sildenafil failures with bremelanotide. Journal of Urology 2023. PMID 36626345. pubmed.ncbi.nlm.nih.gov — concerning Safarinejad MR, Hosseini SY, J Urol 2008;179:1066–1071.
11. RETRACTED: Evaluation of the safety and efficacy of bremelanotide in female subjects with arousal disorder. Journal of Sexual Medicine 2008. PMID 18179455. pubmed.ncbi.nlm.nih.gov
12. Health Canada. Think twice before injecting peptides bought online. Public advisory, 9 April 2026. recalls-rappels.canada.ca
13. Federal Register. Pharmacy Compounding Advisory Committee, notice of meeting, 16 April 2026, docket FDA-2025-N-6895. federalregister.gov — the seven substances heard, none of them bremelanotide.
14. World Anti-Doping Agency. The 2026 Prohibited List, section S0, in force 1 January 2026.
15. National Institutes of Health. LiverTox: bremelanotide. ncbi.nlm.nih.gov

Listed rather than hidden, the things we could not check. We could not query Health Canada's Drug Product Database or Prescription Drug List — both were unreachable — so our Canadian statement is an absence of found evidence, not a confirmed null. We could not open the retraction notice or the Expression of Concern, so we report that they exist and not why. We could not read Diamond 2005, the commentary disputing Spielmans, or the Hadley paper cited for the Melanotan II metabolite relationship — the structural difference between the two molecules is independently confirmed, the metabolite claim is not. Our reading that WADA's S0 does not capture bremelanotide is a reading of the published text, not a ruling. And no supplier publishes a mass for the trifluoroacetate form, so our peptide-content range is arithmetic rather than sourced.