PT-141 vs Viagra: How They Differ
PT-141 (bremelanotide) and Viagra (sildenafil) act at opposite ends of the sexual response. Sildenafil is a PDE5 inhibitor that works on blood flow in erectile tissue and depends on sexual stimulation to have an effect; PT-141 is a melanocortin receptor agonist that acts in the brain, on the pathways tied to desire and arousal. Sildenafil is an approved prescription medicine for erectile dysfunction. Bremelanotide was approved in the United States in 2019 in one injectable form for low sexual desire in premenopausal women, and the PT-141 we supply is a research compound. Here is how the two differ in mechanism and what the human trials of each found.
Findings
- Sildenafil selectively inhibits PDE5, the main phosphodiesterase in human erectile tissue, protecting the cGMP signal that nitric oxide uses to relax smooth muscle (1996).
- In a 12-week double-blind study of 329 men, 69% of intercourse attempts succeeded on sildenafil against 22% on placebo over the final four weeks (1998).
- PT-141 is a cyclic seven-amino-acid analogue of alpha-MSH whose most relevant target is the MC4 receptor in the hypothalamus.
- Two identical phase 3 trials randomising 1,267 premenopausal women with low sexual desire found significant gains in desire and falls in related distress against placebo over 24 weeks (2019).
- In men whose response to sildenafil was inadequate, PT-141 still produced statistically significant erectile responses in the laboratory (2004).
What is sildenafil?
Sildenafil is a small synthetic molecule, not a peptide. In human erectile tissue the dominant phosphodiesterase is PDE5, and sildenafil inhibits it selectively. Because erection depends on nitric oxide and its messenger, cyclic GMP, blocking the enzyme that breaks down cGMP lets the signal last longer (Boolell et al., Int J Impot Res, 1996). The drug does not start that signal itself: the nitric oxide release comes from sexual stimulation, so sildenafil increases the response to stimulation rather than creating one (Goldstein et al., N Engl J Med, 1998). Oral bioavailability averaged 41% in healthy men (Nichols et al., Br J Clin Pharmacol, 2002), and the prescribing information gives a terminal half-life of about 3 to 5 hours.
The human trials of sildenafil
The first controlled evidence came from 12 men with erectile dysfunction of no established organic cause. In a double-blind crossover design, the duration of strong rigidity during visual sexual stimulation rose with each step up in dose, and 10 of 12 men reported better erectile activity on sildenafil against 2 of 12 on placebo (Boolell et al., Br J Urol, 1996).
The pivotal paper followed in 1998. A 24-week dose-response study of 532 men found that erectile function scores improved as the dose increased. A separate 12-week study of 329 men recorded 5.9 successful attempts a month on sildenafil against 1.5 on placebo, and 92% of the 225 men who entered a 32-week open-label extension completed it. Headache, flushing and dyspepsia were the most common adverse effects, in 6% to 18% of men (Goldstein et al., N Engl J Med, 1998). A trial in 781 women with arousal disorder found no significant difference from placebo on any end point (Basson et al., J Womens Health Gend Based Med, 2002).
What is PT-141?
PT-141, now called bremelanotide, is a synthetic cyclic heptapeptide modelled on alpha-melanocyte-stimulating hormone (alpha-MSH). It is an agonist at the melanocortin MC3 and MC4 receptors (Diamond et al., J Sex Med, 2006). MC4 receptors are concentrated in the medial preoptic area of the hypothalamus, and animal studies suggest bremelanotide acts there to increase the release of dopamine, an excitatory transmitter for sexual desire (Pfaus et al., CNS Spectr, 2022). It grew out of the Melanotan II programme, covered in Melanotan II: the clinical history and the PT-141 connection.
The human trials of PT-141
Early work was in men. With intranasal PT-141, erectile responses measured by RigiScan were statistically significant against placebo in healthy men and in men with mild to moderate erectile dysfunction who responded to sildenafil, with the first erection at about 30 minutes and a half-life of roughly two hours (Diamond et al., Int J Impot Res, 2004). Given subcutaneously, it produced significant erections in healthy men without any visual sexual stimulation, and in men with an inadequate response to sildenafil (Rosen et al., Int J Impot Res, 2004).
Development then moved to women. In a crossover study of 18 premenopausal women with sexual arousal disorder, more reported moderate or high desire after PT-141 than after placebo (Diamond et al., J Sex Med, 2006); vaginal blood flow during erotic video did not differ, which fits a central rather than a vascular action. The two RECONNECT phase 3 trials then randomised 1,267 women to bremelanotide or placebo for 24 weeks, with significant increases in desire and reductions in distress in each trial and in the combined analysis (Kingsberg et al., Obstet Gynecol, 2019). Across the programme, nausea (40% against 1.3% on placebo), flushing and headache were the most common adverse events, and ambulatory monitoring recorded small, transient rises in blood pressure (Clayton et al., J Womens Health, 2022). The approval history is summarised by Dhillon and Keam (Drugs, 2019), and the full trial record is in PT-141 human studies.
How do PT-141 and Viagra compare side by side?
| Question | PT-141 (bremelanotide) | Viagra (sildenafil) |
|---|---|---|
| What is it? | Synthetic cyclic peptide, alpha-MSH analogue | Small-molecule drug |
| Size | Seven amino acids | Not a peptide |
| Mechanism | MC3 and MC4 receptor agonist in the brain | PDE5 inhibitor in erectile tissue |
| Needs sexual stimulation? | No: erections recorded without visual stimulation in healthy men | Yes: amplifies the nitric oxide signal from stimulation |
| Main research area | Sexual desire and arousal | Erectile dysfunction |
| Human evidence | Phase 3 trials in 1,267 women; phase 1 and 2 studies in men | Large randomised trials in men from 1996 on |
| Status | Research compound (one approved injectable form in the US) | Approved prescription medicine |
| Forms we supply | Lyophilised vial and nasal spray | Not supplied |
Why the mechanism difference matters for research
- Where the effect starts: sildenafil acts downstream, on the vascular step of erection; PT-141 acts upstream, in the hypothalamic circuits that regulate desire. That is why their trials measured different things: erectile function scores and successful attempts for sildenafil, desire and distress scores for bremelanotide.
- Dependence on stimulation: sildenafil’s studies were built around sexual stimulation, while the 2004 PT-141 studies recorded erections without it, a useful distinction when a design needs to separate central from peripheral effects.
- Populations: sildenafil’s pivotal evidence is in men; bremelanotide’s phase 3 evidence is in premenopausal women.
No published trial has compared the two head to head, so any comparison of strength rests on separate studies with different end points. Related melanocortin and hormone research is covered in PT-141 vs Oxytocin and PT-141 vs Melanotan II.
How is PT-141 supplied?
We supply PT-141 as a 10 mg lyophilised vial and as a ready-mixed PT-141 Nasal Spray in 10 mg and 20 mg bottles, a metered pump delivering 0.175 mL per press. Vials are reconstituted with bacteriostatic water (see the PT-141 reconstitution guide, which includes a calculator), and storage is covered in How long does PT-141 last?. Certificates of analysis are on the lab reports page, and every order ships from within Canada by Canada Post Xpresspost.
PT-141 is supplied for laboratory research use only. The studies above were clinical research using pharmaceutical preparations. Sildenafil is a prescription medicine, and nothing here compares the two for personal use.
Frequently asked questions
What is the difference between PT-141 and Viagra?
Sildenafil is a PDE5 inhibitor that strengthens the blood-flow response of erectile tissue to sexual stimulation. PT-141 (bremelanotide) is a seven-amino-acid melanocortin receptor agonist that acts in the brain, on pathways linked to sexual desire and arousal.
Is PT-141 stronger than Viagra?
That has not been tested. No published trial has compared them directly, and their studies measured different outcomes: erectile function for sildenafil, and desire and distress scores in women for bremelanotide’s phase 3 trials.
Has PT-141 been studied in men who do not respond to Viagra?
Yes. A 2004 study gave PT-141 subcutaneously to men with an inadequate response to sildenafil and recorded statistically significant erectile responses against placebo during visual sexual stimulation.
Does PT-141 work without sexual stimulation?
In a 2004 study of healthy men, subcutaneous PT-141 produced significant erections measured by RigiScan without visual sexual stimulation. Sildenafil, by contrast, amplifies the nitric oxide signal that stimulation produces.
Where can I buy PT-141 in Canada?
Vistara Labs supplies PT-141 as a 10 mg lyophilised vial and a ready-mixed nasal spray, with certificates of analysis, shipped from within Canada by Canada Post Xpresspost. See Buy PT-141 in Canada.
Product details from vistaralabs.ca, October 2026. Sources: Boolell M et al. Sildenafil: an orally active type 5 cyclic GMP-specific phosphodiesterase inhibitor for the treatment of penile erectile dysfunction. Int J Impot Res. 1996. PMID 8858389. Boolell M et al. Sildenafil, a novel effective oral therapy for male erectile dysfunction. Br J Urol. 1996. PMID 8813924. Goldstein I et al. Oral sildenafil in the treatment of erectile dysfunction. N Engl J Med. 1998. PMID 9580646. Nichols DJ et al. Pharmacokinetics of sildenafil after single oral doses in healthy male subjects. Br J Clin Pharmacol. 2002. PMID 11879254. Viagra prescribing information (pharmacokinetics). SAHPRA. Basson R et al. Efficacy and safety of sildenafil citrate in women with sexual dysfunction associated with female sexual arousal disorder. J Womens Health Gend Based Med. 2002. PMID 12150499. Diamond LE et al. Double-blind, placebo-controlled evaluation of intranasal PT-141 in healthy males and patients with mild-to-moderate erectile dysfunction. Int J Impot Res. 2004. PMID 14963471. Rosen RC et al. Evaluation of subcutaneously administered PT-141 in healthy male subjects and in patients with an inadequate response to Viagra. Int J Impot Res. 2004. PMID 14999221. Diamond LE et al. An effect on the subjective sexual response in premenopausal women with sexual arousal disorder by bremelanotide (PT-141). J Sex Med. 2006. PMID 16839319. Pfaus JG et al. The neurobiology of bremelanotide for the treatment of hypoactive sexual desire disorder in premenopausal women. CNS Spectr. 2022. PMID 33455598. Kingsberg SA et al. Bremelanotide for the treatment of hypoactive sexual desire disorder: two randomized phase 3 trials. Obstet Gynecol. 2019. PMID 31599840. Clayton AH et al. Safety profile of bremelanotide across the clinical development program. J Womens Health. 2022. PMID 35147466. Dhillon S, Keam SJ. Bremelanotide: first approval. Drugs. 2019. PMID 31429064.
More on this: Peptides for Libido: What the Research Shows.
All products supplied by Vistara Labs are intended for laboratory research use only. They are not drugs, are not approved for human or veterinary use, and are not intended to diagnose, treat, cure or prevent any condition. Nothing on this page constitutes medical advice or guidance for use in humans.
