Erectile dysfunction: treatment and peptide evidence

What is erectile dysfunction and how common is it?

Erectile dysfunction (ED, ICD-10 N52) is defined as the persistent inability to attain and maintain an erection sufficient to permit satisfactory sexual performance³. It is common in ageing men: the Massachusetts Male Aging Study, a community cohort of more than 1,000 men, described ED as a common biobehavioral phenomenon and estimated that its magnitude will grow as the world population ages¹.

Its clinical importance goes beyond sexual life. An erection depends on healthy endothelium, intact nerves, hormones and emotional state, so ED can be the first sign of vascular disease. Its role as a marker of later cardiovascular disease has been discussed for decades¹, and the Princeton IV consensus (2024) concludes that men with ED should be treated as at risk for cardiac events until proven otherwise⁵.

Symptoms and diagnosis of erectile dysfunction

The core symptom is persistent difficulty starting or sustaining an erection. In clinical trials it is usually quantified with the International Index of Erectile Function (IIEF); for example, a randomized study in obese men defined ED as a score of 21 or less⁹. The visit should also explore desire, ejaculation, mood, the relationship and the patient's medications.

The European Association of Urology (EAU) guidelines describe a basic diagnostic approach for every patient and an advanced one for selected cases, together with a treatment algorithm personalized by invasiveness, tolerability and effectiveness³⁴. The Princeton IV consensus, which updates Princeton III from 2012, adds cardiovascular risk stratification, including coronary artery calcium scoring, for men with ED⁵²⁶.

Standard treatment of erectile dysfunction today

The American Urological Association (AUA, 2018) guideline makes shared decision-making the cornerstone: all patients should be informed of all treatment modalities that are not contraindicated, regardless of invasiveness, as potential first-line treatments, and the man and his partner should understand the benefits and burdens of each². The EAU adopts the same principle of full counselling³.

Lifestyle changes. In a randomized trial of 110 obese men aged 35 to 55, a program of weight loss and more physical activity over 2 years raised the mean IIEF score from 13.9 to 17, while the control group stayed flat (13.5 to 13.6); 17 of 55 men in the intervention group and 3 of 55 controls reached a score of 22 or higher⁹.

PDE5 inhibitors. Sildenafil changed treatment in 1998: in two double-blind studies, 69% of intercourse attempts were successful with sildenafil versus 22% with placebo⁶. A network meta-analysis of 179 randomized trials and 50,620 patients found that all PDE5 inhibitors were significantly more effective than placebo, and its authors concluded that low-dose sildenafil and tadalafil should be the first options⁷. A safety review concludes that PDE5 inhibitors should still be considered first-line therapy for most causes of ED⁸.

Other modalities. The guidelines include options for men who do not respond to or cannot use these drugs, and the AUA stresses that none should be ruled out up front because of invasiveness². The choice depends on the cause, comorbidities and the couple's preferences.

What has peptide research shown?

A 2026 systematic review (PRISMA) gathered 12 studies with 372 men on peptides and male sexual function: melanocortin agonists (PT-141 and melanotan II), kisspeptin analogues and oxytocin. Its authors conclude that melanocortin agonists have the most consistent evidence for improving erectile outcomes, but that samples are small, populations heterogeneous, follow-up short and comparative studies lacking¹¹.

PT-141 (bremelanotide) in men. It is a synthetic α-MSH analog that acts on central nervous system melanocortin receptors, mainly MC4R, not on the vascular pathway of PDE5 inhibitors¹³¹⁴¹². A RigiScan-measured erectile response versus placebo has been shown with the intranasal route in healthy men and in men with mild-to-moderate ED, with the first erection at about 30 minutes¹⁷. By the subcutaneous route, a significant erectile response was observed in healthy men and also in patients with an inadequate response to sildenafil¹⁸. In 19 men who responded to a PDE5 inhibitor, combining it with a low sildenafil dose produced a greater response than sildenafil alone¹⁹. The trial with the most participants (342 sildenafil non-responders) reported positive results in 33.5% versus 8.5% with placebo, but in 2023 the journal published an expression of concern about that article, and another bremelanotide trial by the same author, in women, was retracted²⁰²¹. A closer look is in PT-141 in men: a central, not vascular, mechanism.

Melanotan II. This is the compound PT-141 derives from. In a double-blind crossover trial in 10 men with psychogenic ED, 8 of 10 had clinically apparent erections¹⁵; in 10 men with organic risk factors, patient-reported erections followed 12 of 19 injections versus 1 of 21 with placebo, with frequent nausea¹⁶. These are studies from 1998 and 2000 with 10 participants each. See Melanotan II and PT-141: chemical cousins, opposite stories.

Kisspeptin. In a randomized, double-blind crossover trial of 37 men with hypoactive sexual desire (32 completed), intravenous kisspeptin-54 infusion modified brain activity in the sexual-processing network versus placebo and was associated with greater penile tumescence (up to 56% more) in response to sexual stimuli; it is not an ED trial and did not use rigidity as its primary outcome²⁵. More context in Kisspeptin: real science, wrong molecule?.

Oxytocin. The 2026 review describes mixed effects: possible benefits on orgasm intensity and sexual satisfaction, with no consistent improvement in erectile function¹¹.

Safety and contraindications

PDE5 inhibitors. In the pivotal sildenafil trial, headache, flushing and dyspepsia were the most common adverse events, in 6% to 18% of men⁶. The network meta-analysis found more visual disorders with high-dose sildenafil and more nasal congestion with vardenafil and udenafil⁷. A safety review reports a favorable cardiovascular profile when they are used according to the Princeton consensus, a small increase in the risk of non-arteritic anterior ischemic optic neuropathy, and a weak, controversial association with melanoma⁸. The interaction between nitrates and PDE5 inhibitors is a central safety consideration and has been revisited in the cardiovascular literature¹⁰. Counterfeit medicines claiming to contain these active ingredients are a public health problem described in the same review⁸.

Bremelanotide. The Vyleesi label warns of a transient rise in blood pressure (up to 6 mmHg systolic and 3 mmHg diastolic at the approved dose) and contraindicates it in uncontrolled hypertension or known cardiovascular disease; nausea was the most common reaction (40% versus 1% with placebo) and focal hyperpigmentation was reported²⁴. In a randomized trial with ambulatory monitoring in 397 women, subcutaneous bremelanotide produced small, transient rises in blood pressure accompanied by a lower heart rate²². Bremelanotide is not indicated in men²⁴; its approval rested on two phase 3 trials (RECONNECT) in 1,267 women²³.

Kisspeptin and oxytocin. There are no long-term safety data in men for these uses; the available evidence comes from small, short studies¹¹²⁵.

Summary by agent

• PDE5 inhibitors (sildenafil, tadalafil and others): status: standard of care; best evidence: very large randomized trials and meta-analyses⁶⁷; main caution: nitrate interaction, headache, flushing, visual disorders⁶⁸¹⁰.
• PT-141 (bremelanotide): status: human phase 1–2 trials, not approved in men; best evidence: erectile response in healthy men and in men with an inadequate sildenafil response¹⁷¹⁸; main caution: transient blood pressure rise, nausea, hyperpigmentation²⁴.
• Melanotan II: status: only small studies from 1998 and 2000; best evidence: erections in 8 of 10 men with psychogenic ED¹⁵; main caution: frequent nausea¹⁶.
• Kisspeptin: status: human mechanism trial, no ED trials; best evidence: greater tumescence and activation of the brain's sexual network²⁵; main caution: small sample, short duration²⁵.
• Oxytocin: status: mixed effects; best evidence: possible benefit on orgasm and satisfaction, no consistent erectile improvement¹¹.

Frequently asked questions

Is erectile dysfunction always psychological? No. It can be vascular, neurological, hormonal, psychogenic or mixed; the trials include organic, psychogenic and mixed causes⁶. It can also be an early warning of cardiovascular disease, which is why the Princeton IV consensus calls for cardiac risk stratification⁵.

What is the first-line treatment? The guidelines call for shared decision-making and for presenting every option that is not contraindicated²³; among drugs, PDE5 inhibitors remain first line in most cases⁸.

Do lifestyle changes help? Yes, in some patients: in obese men, weight loss and more physical activity over 2 years were associated with improvement in about one third of them⁹.

Is any peptide approved for erectile dysfunction? No. Bremelanotide is FDA-approved only for hypoactive sexual desire disorder in premenopausal women, and its label says it is not indicated in men²⁴.

What does the evidence say about PT-141 in men? An erectile response versus placebo has been shown in small trials, including in some men with an inadequate sildenafil response, but the largest trial carries an expression of concern and there are no recent phase 3 studies in men¹⁷¹⁸²⁰.

Does kisspeptin treat erectile dysfunction? It has not been studied as an ED treatment; the only randomized trial cited here was done in men with hypoactive sexual desire and measured brain and tumescence changes²⁵.