PT-141 is bremelanotide, and bremelanotide is an approved medicine — Vyleesi, a single-use autoinjector — so its side effects were measured rather than reported by users. The catch is who they were measured in: premenopausal women with a diagnosed desire disorder, using it a few times a month. Most of the PT-141 sold online is bought by other people, for other reasons, at other frequencies. This page reports what the label counted, what FDA's adverse-event database adds, and the gaps between the two. The dose itself is covered on our PT-141 dosage page.
The trials behind the rates
The Vyleesi label (NDA 210557, Cosette Pharmaceuticals, effective 2025-11-13 on openFDA) draws on two identical 24-week, randomised, double-blind, placebo-controlled trials in 1,247 premenopausal women, aged 19 to 56 (mean 39), followed by a 52-week open-label extension in which 684 continued. The label notes that most patients used it two to three times a month and no more than once a week — well inside the eight-a-month ceiling. Serious adverse reactions: 1.1% on bremelanotide, 0.5% on placebo.
The label's table
| Reaction | Bremelanotide (n=627) | Placebo (n=620) |
|---|---|---|
| Nausea | 40.0% | 1.3% |
| Flushing | 20.3% | 0.3% |
| Injection-site reactions | 13.2% | 8.4% |
| Headache | 11.3% | 1.9% |
| Vomiting | 4.8% | 0.2% |
| Cough | 3.3% | 1.3% |
| Fatigue | 3.2% | 0.5% |
| Hot flush | 2.7% | 0.2% |
| Paraesthesia | 2.6% | 0.0% |
| Dizziness | 2.2% | 0.5% |
| Nasal congestion | 2.1% | 0.5% |
Below 2%, and more often than on placebo: upper abdominal pain, diarrhoea, muscle and joint pain, restless legs, runny nose, raised creatine kinase, raised blood pressure, limb pain and focal skin darkening. Most events were rated mild (31%) or moderate (40%) and transient.
The number that stands out is the dropout rate: 18% of women on bremelanotide stopped because of an adverse reaction, against 2% on placebo — nausea alone accounted for 8 points of it, headache 2.
Nausea, specifically
Nausea is the defining side effect, and the label describes it in detail. Median onset within one hour, lasting about two hours. It was highest after the first dose (21%) and fell to about 3% after later ones. 13% of patients were given an anti-emetic.
One detail is worth knowing because it is counter-intuitive: in a phase 4 study, 228 healthy women were given 8 mg of oral ondansetron or placebo 30 minutes before a 1.75 mg dose, and there was no difference in nausea. The label concludes that pre-treatment with oral ondansetron "is not recommended", and that treating nausea after it starts has not been formally studied.
Blood pressure and heart rate
Bremelanotide raises blood pressure after every dose. The label's figures: maximal increases of 6 mmHg systolic and 3 mmHg diastolic, peaking 2 to 4 hours after the dose, with heart rate falling by up to 5 beats per minute, usually back to baseline within 12 hours. Daily dosing 24 hours apart for up to 16 days showed no build-up. The label contraindicates it in uncontrolled hypertension or known cardiovascular disease, calls it not recommended for people at high cardiovascular risk, and ties the one-dose-in-24-hours limit to this effect.
Pigmentation — where frequency changes everything
Bremelanotide acts on melanocortin receptors, the family that controls skin pigment, and it is a close chemical relative of melanotan II. The label reports two very different rates:
| Exposure | New focal hyperpigmentation |
|---|---|
| Up to 8 doses a month, 24-week trials | 1% (0% on placebo) |
| 8 consecutive daily doses | 38% |
| 8 further daily doses in those who continued | 14% more |
The patches appeared on the face, gums and breasts, were more likely in darker skin, and "resolution … was not confirmed in all patients after discontinuation." The monthly limit on the label — more than eight doses "is not recommended" — rests on this finding. The daily-use figure is the one that matters for anyone using PT-141 outside that pattern; the parallel record for the tanning compounds is on our melanotan 2 dosage page.
One case of liver injury, and one interaction
In the open-label extension, a woman who had received 10 doses over a year developed acute hepatitis — transaminases above 40 times the upper limit, bilirubin six times — which resolved four months after stopping; the label says the role of bremelanotide could not be excluded. Separately, the label warns that bremelanotide may slow gastric emptying and significantly lower blood levels of oral naltrexone, and says to avoid combining them when naltrexone is being used for alcohol or opioid dependence.
What FDA's adverse-event database holds
An openFDA FAERS query on 2026-09-28 (data updated 2026-07-30) returned 1,004 reports naming bremelanotide. Where sex was recorded, 883 were women and 50 men; 31 were coded serious. The most frequent terms mirror the label:
| Term | Reports |
|---|---|
| Nausea | 432 |
| Drug ineffective | 202 |
| Headache | 148 |
| Vomiting | 115 |
| Off-label use | 94 |
| Flushing | 72 |
| Illness | 72 |
| Dizziness | 43 |
"Off-label use" in 94 reports is the market outside the label showing up in the pharmacovigilance record. FAERS counts cannot give a rate; they show what was reported, not how often it happens.
The gap: men
The label excludes men explicitly, and no registered trial of bremelanotide for erectile problems appears on ClinicalTrials.gov. The male data that exist are older and mostly intranasal, at doses of 10–20 mg that are not comparable with the 1.75 mg injection. The largest efficacy study, a 2008 trial of 342 men who had not responded to sildenafil, gave 10 mg intranasally and reported "more drug related adverse effects" than placebo without rates in its abstract; the Journal of Urology attached an expression of concern to it in 2023. A 2017 phase 1 study gave 20 mg intranasally to 12 men and 12 women alongside alcohol. None of this is a side-effect profile for men using a research vial.
What the record does not contain
- Any adverse-event rate in men.
- Rates for daily use beyond 16 days, apart from the pigmentation study.
- Anything about the contents of PT-141 vials sold as research chemicals, which are not Vyleesi and carry none of its manufacturing controls — see our note on what research-use-only labelling means.
Anyone weighing bremelanotide, or connecting a symptom to it, should take the question to a prescriber; the label is the document to bring. The broader set of records is indexed on our peptide side-effects overview.
Sources and dates
- VYLEESI (bremelanotide) injection, Cosette Pharmaceuticals, Inc., NDA 210557. openFDA drug label, set id f1d0c1b5-2f39-4bad-a6a4-0066e3ad5dcf, effective 2025-11-13. Sections 4, 5, 6.1, 7. Read 2026-09-28.
- openFDA drug adverse event endpoint, generic name "bremelanotide": total, counts by sex, seriousness and reaction term, run 2026-09-28 (dataset updated 2026-07-30).
- Safarinejad MR, Hosseini SY. Salvage of sildenafil failures with bremelanotide: a randomized, double-blind, placebo controlled study. J Urol. 2008;179(3):1066-71. PMID 18206919 (expression of concern, J Urol 2023).
- Clayton AH, Lucas J, DeRogatis LR, Jordan R. Phase I randomized placebo-controlled, double-blind study of the safety and tolerability of bremelanotide coadministered with ethanol in healthy male and female participants. Clin Ther. 2017;39(3):514-526. PMID 28189361.
- ClinicalTrials.gov search, intervention "bremelanotide": 10 registered studies, none recruiting, and none under an erectile-dysfunction condition, on 2026-09-28.