PT-141 vs Melanotan II: How They Differ
PT-141 (bremelanotide) and Melanotan II are near-identical cyclic peptides: they differ only at the last atom group of the chain, where Melanotan II ends in an amide and PT-141 in a carboxylic acid. Melanotan II is a non-selective melanocortin agonist first studied for tanning, and its effect on erections in those studies led to PT-141, which was developed for sexual desire and approved in the United States in 2019. Here is how the two compare, what the human studies on each found, and where the PT-141 Nasal Spray and the Melanotan II Nasal Spray fit.
Findings
- One functional group separates them. PubChem lists Melanotan II as C50H69N15O9 with a C-terminal carboxamide and bremelanotide as C50H68N14O10 with a C-terminal carboxylic acid; the seven-residue ring is the same.
- In 20 men with erectile dysfunction, Melanotan II produced erections in 17 without sexual stimulation, and raised reported desire after 68% of doses against 19% of placebo doses (2000).
- PT-141’s development moved from erectile studies in men to women: two phase 3 trials randomised 1,267 premenopausal women with hypoactive sexual desire disorder and found significant gains in desire and falls in related distress (2019).
- Melanotan II’s first human study recorded measurable tanning after five low doses; with PT-141, focal darkening of the skin was rare at labelled use (2022 safety review).
What is Melanotan II?
Melanotan II (MT-II) is a lactam-bridged cyclic heptapeptide analogue of alpha-melanocyte stimulating hormone (alpha-MSH), the hormone that drives skin pigmentation. Researchers at the University of Arizona built it for potency at melanocortin receptors and ran a pilot phase 1 study in 1996: three healthy men received it by subcutaneous injection over two weeks, two showed increased pigmentation of the face, upper body and buttocks a week after the last dose, and the team recorded spontaneous erections that came with a stretching and yawning complex (Dorr et al., Life Sci, 1996).
The erectile studies
That observation became its own line of research. In a double-blind, placebo-controlled crossover study of 10 men with psychogenic erectile dysfunction, Melanotan II produced clinically apparent erections in 8 of them; mean time at more than 80% tip rigidity was 38.0 minutes against 3.0 with placebo (Wessells et al., J Urol, 1998). A second study in 10 men with organic risk factors found erections after 12 of 19 Melanotan II injections against 1 of 21 placebo doses, with sexual desire significantly higher after the peptide (Wessells et al., Urology, 2000).
The group’s summary of all 20 men described Melanotan II as a non-selective melanocortin receptor agonist: it led to erection in 17 of 20 without sexual stimulation, and increased desire was reported after 13 of 19 doses (68%) against 4 of 21 placebo doses (19%). Nausea and yawning were the frequent side effects (Wessells et al., Int J Impot Res, 2000). The full background is in Melanotan II: the clinical history and the PT-141 connection.
What is PT-141?
PT-141, now named bremelanotide, is the same seven-residue ring as Melanotan II with a free acid at the C-terminus in place of the amide. PubChem records the two as compounds 92432 (Melanotan II, molecular weight 1024.2) and 9941379 (bremelanotide, 1025.2), with identical stereochemistry and side chains. Its developer described it as an agonist at melanocortin receptors including MC3R and MC4R, expressed mainly in the central nervous system, and reported that in rats it activated hypothalamic neurons linked to the penis (Molinoff et al., Ann N Y Acad Sci, 2003). A later review describes high affinity for the MC4 receptor, the one thought to matter for sexual function (Dhillon and Keam, Drugs, 2019).
From a nasal spray in men to trials in women
PT-141’s first human program used an intranasal form. In healthy men and in men with mild-to-moderate erectile dysfunction, intranasal PT-141 produced statistically significant erectile responses at doses above 7 mg, with the first erection at about 30 minutes and a half-life of 1.85 to 2.09 hours (Diamond et al., Int J Impot Res, 2004). In 19 men with erectile dysfunction, a low intranasal dose added to 25 mg sildenafil gave a significantly greater erectile response than sildenafil alone (Diamond et al., Urology, 2005).
Development then shifted to subcutaneous injection in women. The two identical phase 3 trials randomised 1,267 premenopausal women with hypoactive sexual desire disorder to bremelanotide or placebo for 24 weeks, and both found statistically significant increases in sexual desire and reductions in distress about low desire (Kingsberg et al., Obstet Gynecol, 2019). In the 52-week open-label extension, 684 women continued and the improvements held, with no new safety signals (Simon et al., Obstet Gynecol, 2019). Nausea was the most common side effect, at 40.0% against 1.3% on placebo (Clayton et al., J Womens Health, 2022). The trial record is covered in PT-141 human studies.
Why does one small change matter?
Swapping the C-terminal amide for an acid is the kind of edit that shifts how a peptide sits in its receptors. Melanotan II’s own investigators called it non-selective, and its first study was a tanning study. PT-141 was carried forward for its central effects on desire. Pigmentation did not disappear entirely: the 2022 safety review found focal hyperpigmentation rare at labelled use, but present in more than a third of participants after up to 16 consecutive daily doses (Clayton et al., J Womens Health, 2022). The two have not been compared head to head in a published human trial.
How do PT-141 and Melanotan II compare side by side?
| Question | PT-141 | Melanotan II |
|---|---|---|
| What is it? | Cyclic alpha-MSH analogue, C-terminal acid | Cyclic alpha-MSH analogue, C-terminal amide |
| Size | Seven residues (molecular weight 1025.2) | Seven residues (molecular weight 1024.2) |
| Main research area | Sexual desire and arousal | Skin pigmentation, then erectile function |
| Mechanism | Melanocortin agonist, high MC4R affinity | Non-selective melanocortin agonist |
| Human evidence | Phase 3 trials, 1,267 women; approved in the US in 2019 | Small phase 1 and crossover studies, 1990s |
| Forms we supply | 10 mg vial; nasal spray in 10 mg and 20 mg | 10 mg vial; 10 mg nasal spray |
Which one fits which research question?
- Sexual desire, central melanocortin signalling and the MC4 receptor: PT-141, which has the large controlled trials and the approval record.
- Pigmentation and the broad melanocortin family: Melanotan II, whose earliest human data are tanning data.
- Structure-activity work: both, since a single terminal group is the only difference between them.
How are PT-141 and Melanotan II supplied?
PT-141 comes as a 10 mg lyophilised vial and as the PT-141 Nasal Spray in two bottle sizes. Melanotan II comes as a 10 mg vial and as the Melanotan II Nasal Spray. The sprays arrive ready-mixed in a sealed metered pump delivering 0.175 mL per press. Vials are reconstituted with bacteriostatic water; see the PT-141 reconstitution guide and the Melanotan II reconstitution guide. PT-141 is also part of the Libido Spray Stack with oxytocin, and of the Libido Trifecta Spray Stack, which adds kisspeptin; Melanotan II is not in either, since it covers the same receptor family as PT-141. Certificates of analysis are on the lab reports page, and every order ships from within Canada.
PT-141 and Melanotan II are supplied for laboratory research use only. The studies above were clinical research using pharmaceutical preparations.
Frequently asked questions
What is the difference between PT-141 and Melanotan II?
They share the same seven-residue cyclic structure. Melanotan II ends in an amide and PT-141 (bremelanotide) in a carboxylic acid. Melanotan II is a non-selective melanocortin agonist first studied for tanning; PT-141 was developed for sexual desire and has phase 3 trials behind it.
Is PT-141 stronger than Melanotan II?
No published human trial has compared them directly, so neither can be called stronger. Melanotan II produced erections in 17 of 20 men in 1990s crossover studies; PT-141 was tested in phase 3 trials of 1,267 women and approved in the United States in 2019.
Is PT-141 a metabolite of Melanotan II?
Structurally, PT-141 is Melanotan II with the C-terminal amide replaced by a carboxylic acid, which is why it is often described that way. PubChem lists them as separate compounds that differ only at that position.
Does PT-141 cause tanning like Melanotan II?
Much less. A 2022 review of the bremelanotide program found focal hyperpigmentation rare at labelled use, though it appeared in more than a third of participants after up to 16 consecutive daily doses. Melanotan II produced measurable tanning after five low doses in its first study.
Where can I buy PT-141 and Melanotan II in Canada?
Vistara Labs supplies both as lyophilised vials and ready-mixed nasal sprays, shipped from within Canada by Canada Post Xpresspost. PT-141 is also in the Libido Spray Stack and the Libido Trifecta Spray Stack.
Product details from vistaralabs.ca, October 2026. Sources: Dorr RT et al. Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Life Sci. 1996. PMID 8637402. Wessells H et al. Synthetic melanotropic peptide initiates erections in men with psychogenic erectile dysfunction: double-blind, placebo controlled crossover study. J Urol. 1998. PMID 9679884. Wessells H et al. Effect of an alpha-melanocyte stimulating hormone analog on penile erection and sexual desire in men with organic erectile dysfunction. Urology. 2000. PMID 11018622. Wessells H et al. Melanocortin receptor agonists, penile erection, and sexual motivation: human studies with Melanotan II. Int J Impot Res. 2000. PMID 11035391. Molinoff PB et al. PT-141: a melanocortin agonist for the treatment of sexual dysfunction. Ann N Y Acad Sci. 2003. PMID 12851303. Dhillon S, Keam SJ. Bremelanotide: first approval. Drugs. 2019. PMID 31429064. Diamond LE et al. Double-blind, placebo-controlled evaluation of the safety, pharmacokinetic properties and pharmacodynamic effects of intranasal PT-141. Int J Impot Res. 2004. PMID 14963471. Diamond LE et al. Co-administration of low doses of intranasal PT-141 and sildenafil to men with erectile dysfunction results in an enhanced erectile response. Urology. 2005. PMID 15833522. Kingsberg SA et al. Bremelanotide for the treatment of hypoactive sexual desire disorder: two randomized phase 3 trials. Obstet Gynecol. 2019. PMID 31599840. Simon JA et al. Long-term safety and efficacy of bremelanotide for hypoactive sexual desire disorder. Obstet Gynecol. 2019. PMID 31599847. Clayton AH et al. Safety profile of bremelanotide across the clinical development program. J Womens Health. 2022. PMID 35147466. PubChem compound records: bremelanotide, CID 9941379; Melanotan II, CID 92432.
More on this: Melanotan II: The Clinical History and the PT-141 Connection.
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.
