PT-141 vs Viagra: differences, evidence and safety

PT-141 (bremelanotide) activates melanocortin receptors and produced erections in small placebo-controlled studies of men, including men Viagra had not helped. Viagra (sildenafil) works on blood flow in the penis, and its label reports improved erections in 82% of men at the top dose versus 24% on placebo.

On regulatory status, the two are far apart. Viagra has been FDA-approved for erectile dysfunction since 1998, based on 21 randomized trials in more than 3,000 men. Bremelanotide is approved only as Vyleesi, for low sexual desire in premenopausal women, and its label says it is not indicated for men. Its largest trial in men is now under an expression of concern.

Item	PT-141 (bremelanotide)	Viagra (sildenafil)
US FDA status	Approved 2019 as Vyleesi for acquired, generalized HSDD in premenopausal women; not indicated for men or postmenopausal women (label, rev. 3/2024). “PT-141” sold as a research peptide was named in an FDA warning letter dated 2026-08-24 as an unapproved new drug	Approved 1998 for erectile dysfunction in men; “not indicated for use in females” (label)
Compounding	Not named on FDA’s Category 2 list (page current as of 2026-04-22)	Not named on FDA’s Category 2 list (same page)
WADA	Not named in the 2026 List changes (USADA). An approved drug, so outside S0. 2027 List (in force 2027-01-01): text not verified by us	Not named in the 2026 List changes; same 2027 caveat
Strongest evidence	Approved label (women, HSDD); small human controlled studies for erections in men	Approved label (men, ED); 21 RCTs
Human trials	Women: 2 phase 3 RCTs (NCT02333071, NCT02338960). Men with ED: 4 published controlled studies; none registered on ClinicalTrials.gov (searched 2026-11-07)	21 placebo-controlled RCTs, more than 3,000 men (label)
Last checked	2026-11-07	2026-11-07

PT-141 vs Viagra at a glance

Feature	PT-141	Viagra
What it is	Cyclic 7-amino-acid peptide (bremelanotide)	Tablet (sildenafil citrate)
Class	Melanocortin receptor agonist	PDE5 inhibitor
Main target	MC4 receptor	PDE5 in penile tissue
Main research focus	Low desire in women; erections in men (early)	Erectile dysfunction
Human evidence	2 phase 3 RCTs (women); 4 small or disputed studies (men)	21 RCTs (men)
Approval	Vyleesi: premenopausal women only	Men with ED
WADA	Not named (2026)	Not named (2026)
Routes studied	Under the skin (approved); nasal (dropped); IV	By mouth
Onset in studies	First erection about 30 min (nasal, men)	Taken 30 min to 4 h before sex
Main safety concerns	Nausea, flushing, blood pressure rise, skin darkening	Headache, flushing, nitrate interaction, priapism

What is PT-141?

PT-141 is the research code for bremelanotide, a synthetic cyclic peptide that activates melanocortin receptors. The approved label says binding at the MC4 receptor is the most relevant action at therapeutic doses (Vyleesi label). It was first studied as a nasal spray, for erectile dysfunction and for sexual dysfunction in women. In the US it is sold only as Vyleesi, an autoinjector for premenopausal women with acquired, generalized hypoactive sexual desire disorder (HSDD), which means persistent low desire that causes distress. Readers weighing melanotan II against PT-141 will find melanotan II covered in our Melanotan 1 vs Melanotan 2 comparison.

What is Viagra?

Viagra is Pfizer’s brand of sildenafil citrate. It has been approved since 1998 for erectile dysfunction (ED) and is not indicated for women or children. It is a tablet that blocks phosphodiesterase type 5 (PDE5), an enzyme that breaks down cGMP, a chemical messenger in penile tissue. Blocking PDE5 strengthens the nitric oxide signal that lets blood fill the penis during arousal. In the UK the 50 mg Viagra Connect tablet has been a pharmacy medicine without prescription since 2017 for men over 18.

How they work differently

• PT-141: activates melanocortin receptors, and the label names MC4R as the most relevant one (Vyleesi label). Viagra: works on blood vessels in the penis by inhibiting PDE5 (Viagra label).
• PT-141: under the skin, it caused a significant erectile response in healthy men at doses above 1 mg without visual sexual stimulation (Rosen 2004, Human, small controlled study). Viagra: the label says it has no effect without sexual stimulation.
• PT-141: raises blood pressure briefly after each dose. Viagra: can lower blood pressure, especially with alpha-blockers, and must not be used with nitrates.

A common shorthand says PT-141 works on “wanting to” and Viagra on “being able to”. That fits the two mechanisms, but no head-to-head trial has tested it.

Evidence head-to-head

Each figure below comes from a separate trial with its own population and measure. The PT-141 and Viagra numbers are cross-trial, so they cannot be ranked against each other directly.

Outcome	PT-141 best evidence	Viagra best evidence
Erections, men with ED	Human RCT (n=342): positive result 33.5% vs 8.5% placebo; under expression of concern (Safarinejad 2008)	Approved label (4 fixed-dose RCTs, 1,797 men): improved erections 63–82% vs 24% placebo (label)
Successful intercourse	No figure found in published PT-141 trials	Human RCT (n=329): 69% of attempts vs 22% (Goldstein 1998)
Men not helped by Viagra	Human, small crossover: significant response at both doses tested (Rosen 2004)	Not applicable
Lab-measured erections	Human, placebo-controlled: significant above 7 mg nasal (Diamond 2004)	Covered by label RCTs
Low desire, women	Approved label, 2 RCTs (n=1,267): desire score +0.5/+0.6 vs +0.2 (Kingsberg 2019)	Human RCT (n=781): no significant difference vs placebo (Basson 2002)
Satisfying sexual events, women	Approved label: no significant difference vs placebo	Human RCT: no significant difference (Basson 2002)

The strongest PT-141 result in men has a serious integrity problem. In 2023 The Journal of Urology published an expression of concern about the 342-man trial in men who had not responded to sildenafil. A second bremelanotide trial by the same lead author, in women with arousal disorder, has been retracted after reviewers raised “multiple concerning questions about the methodology, results, and statistical interpretation”. Without that trial, the evidence for PT-141 in men rests on the developer’s small early studies. Those studies measured erections in the lab with a RigiScan device, not during everyday sex (Diamond 2004).

Those early results are still encouraging. In the Rosen study, PT-141 produced significant erections in men who could get an erection firm enough for intercourse no more than half the time on 100 mg Viagra (Rosen 2004, Human, small crossover). No phase 3 trial in men followed.

Which fits which goal?

• Erectile dysfunction in men: Viagra has much more evidence. It has 21 RCTs and an approved label, plus subgroup data in diabetes (57% vs 10% improved erections) and spinal cord injury (83% vs 12%) (Viagra label). PT-141’s evidence in men is small, lab-based or under an expression of concern.
• Men for whom Viagra has not worked: PT-141 showed an effect in early, small human studies. No large independent trial has confirmed them.
• Low sexual desire in premenopausal women: PT-141 has more evidence, with two phase 3 RCTs and an approved label. Sildenafil did no better than placebo in women in a large RCT.
• Low desire in men: neither drug is approved for it. We found no registered bremelanotide trial in men on ClinicalTrials.gov (searched 2026-11-07).

For desire-focused options, our page on PT-141 vs kisspeptin for men and women covers the hormone-pathway alternative. Vyleesi vs Addyi compares the two approved desire drugs for women. Heart health, other medicines and the cause of the problem all matter here, and a clinician is the person to decide.

Can PT-141 and Viagra be combined?

One controlled study has tested the combination. It was a randomized crossover study in 19 men with ED who normally responded to Viagra or Levitra. A low nasal dose of PT-141 plus a low dose of sildenafil produced a significantly greater lab-measured erectile response than sildenafil alone, with no new or more frequent side effects than either drug alone (Diamond 2005, Human, single-dose crossover, n=19). That study was a single-dose lab test of a nasal formulation that is no longer in development. We found no registered trial of bremelanotide with sildenafil on ClinicalTrials.gov (searched 2026-11-07). Both labels carry blood pressure warnings, in opposite directions. Vyleesi briefly raises blood pressure, while Viagra can lower it, notably with nitrates or alpha-blockers.

Safety and regulatory status

PT-141 (bremelanotide)

In the Vyleesi phase 3 pool (627 women on the drug, 620 on placebo), the most common side effects were nausea (40.0% vs 1.3%), flushing (20.3% vs 0.3%), injection site reactions (13.2% vs 8.4%), headache (11.3% vs 1.9%) and vomiting (4.8% vs 0.2%) (Vyleesi label). The label also reports that:

• 13% of women needed anti-nausea medicine, and taking ondansetron beforehand did not reduce nausea.
• The label reports maximal increases of 6 mmHg systolic and 3 mmHg diastolic blood pressure after each dose, peaking 2 to 4 hours later, with heart rate falling by up to 5 beats per minute. The drug is contraindicated in uncontrolled hypertension or known cardiovascular disease.
• Focal skin darkening occurred in 1% of women using up to 8 doses a month, and in 38% after 8 days of daily dosing. It did not always clear.
• Bremelanotide can lower blood levels of oral naltrexone.

Blood pressure is the reason the nasal spray disappeared. Palatin’s 2008 10-K says it stopped developing bremelanotide for sexual dysfunction “after the FDA raised concerns about the acceptable benefit/risk ratio of bremelanotide as a first-line therapy for erectile dysfunction, primarily because of increases in blood pressure observed in some patients” (Palatin 10-K). A later paper says the nasal route had “a wide variability in bioavailability”, which is why the under-the-skin form was developed (White 2017). No PT-141 nasal spray is FDA-approved. “PT-141” products sold online as research chemicals are unregulated, and FDA treated one seller’s PT-141 as an unapproved new drug in an August 2026 warning letter.

Viagra (sildenafil)

In the label’s fixed-dose trials, side-effect rates rose with dose (placebo rates in brackets) (Viagra label):

• headache 16–28% (7%)
• flushing 10–19% (2%)
• dyspepsia 3–17% (2%)
• abnormal vision 1–11% (1%)
• nasal congestion 4–9% (2%)

Sildenafil is contraindicated with nitrates and with riociguat. The label also warns about erections lasting more than 4 hours, sudden vision loss (NAION), sudden hearing loss and low blood pressure with alpha-blockers. In the UK, the pharmacy version is not sold to men with severe cardiovascular disorders, high cardiovascular risk, liver failure or severe kidney failure (MHRA).

Athletes

We did not find either drug named in the 2026 WADA List changes (USADA). The S0 catch-all covers only substances “not approved by any government regulatory authority” (USADA), and both drugs are approved. We could not verify the text of the 2027 List, so Global DRO or a national anti-doping agency is the place to confirm.

Anyone who suspects a side effect from PT-141, Viagra or any other drug or product can report it to the FDA through MedWatch.

How long do effects take in studies?

• PT-141 nasal (men): the first erection came about 30 minutes after dosing. Blood levels peaked at a median of 0.5 hours, and the half-life was about 2 hours (Diamond 2004).
• Vyleesi (women): the label directs use at least 45 minutes before anticipated sexual activity. It says to stop if there is no improvement after 8 weeks (label).
• Viagra: taken 30 minutes to 4 hours before sex. One study showed an effect for up to 4 hours, though it was weaker at 4 hours than at 2 (label).