TL;DR: PT-141 (bremelanotide, nicknamed the “female Viagra”) and Melanotan 2 (the “Barbie peptide”) are close relatives — both are melanocortin receptor agonists, and they overlap on the MC4 receptor that drives libido. The difference is what else they hit. PT-141 is aimed at the sexual-function receptors and does little tanning; Melanotan 2 also activates the pigment receptor (MC1R), so it tans as well. In short: PT-141 is the libido-focused cousin, Melanotan 2 is the tanning cousin that shares the libido side effect.
PT-141 and Melanotan 2 are frequently confused because both produce a libido effect and both descend from the same melanocortin family. They are genuinely related — PT-141 is a metabolite-derived relative of Melanotan 2 — but they were developed for different purposes. This guide separates them.
Same Family, Different Target
Both are melanocortin receptor agonists, and the family of receptors they act on governs several different things — pigmentation (MC1R) and sexual function/appetite (MC3R, MC4R). Which receptors each peptide favours is the whole story:
- PT-141 (bremelanotide) targets the MC3/MC4 receptors in the central nervous system, driving sexual desire. It does little at the pigment receptor, so it does not meaningfully tan.
- Melanotan 2 activates MC1R (pigment) plus MC3/MC4R, so it tans and carries the libido/erectile effect as part of its broader profile.
- 1
Shared: MC4R
Both activate the MC4 receptor — the source of the libido effect in each.
- 2
PT-141: stops there
Focused on the sexual-function receptors; minimal tanning.
- 3
Melanotan 2: adds MC1R
Also hits the pigment receptor, so it tans — libido becomes a side effect.
Head-to-Head Comparison
| Feature | PT-141 | Melanotan 2 |
|---|---|---|
| Brand/INN | Bremelanotide, Vyleesi | none (never approved) |
| Nicknames | ”female Viagra”, “libido peptide" | "Barbie peptide”, “tan jab” |
| Primary purpose | Sexual desire | Tanning |
| Tanning effect | Minimal | Yes |
| Libido effect | Primary | Present (side effect) |
| Regulatory status | Approved (Vyleesi, for HSDD) | Not approved |
Qualitative from the research literature; both share the libido effect via MC4R.
Which One For Which Question
The practical distinction is straightforward:
- If the research interest is sexual function, PT-141 is the targeted tool — it is approved as Vyleesi for hypoactive sexual desire disorder and does not carry the tanning or pigmentation effects. See PT-141 dosing and side effects.
- If the research interest is tanning, Melanotan 2 is the compound — but its MC4R activity means a libido/erectile effect comes along with it, which is exactly why the “Barbie peptide” nickname bundles tan, appetite, and libido together. See Melanotan 2 dosing and Melanotan 1 vs Melanotan 2.
Using Melanotan 2 for libido is using a tanning compound for its side effect — PT-141 is the more selective option for that purpose. Research vials are available for PT-141 (10mg) and Melanotan 2 (10mg); model any dose in the reconstitution calculator.
Side Effects
Both share the melanocortin side-effect signature, weighted differently:
- Both: nausea and facial flushing, dose-dependent — the MC-agonist hallmark.
- Melanotan 2 additionally: pigmentation effects — darkening of moles and freckles (see melanotan, moles and freckles) — which PT-141 does not cause.
Safety, Legality & Research Disclaimers
PT-141 is approved as a medicine (Vyleesi) for a specific indication; Melanotan 2 is not approved anywhere. Both are handled here as research peptides, not for self-administration outside appropriate oversight. They are laboratory research chemicals for qualified individuals and legitimate research purposes only. Regulatory status varies by jurisdiction; researchers are responsible for compliance with applicable local laws and institutional requirements. Nothing here is medical advice.
FAQ
Are PT-141 and Melanotan 2 the same thing?
No, but they are close relatives. Both are melanocortin receptor agonists and both produce a libido effect through the MC4 receptor. The difference is that PT-141 (bremelanotide) is focused on the sexual-function receptors and does little tanning, while Melanotan 2 also activates the pigment receptor (MC1R) and tans.
Why is PT-141 called the “female Viagra”?
Because it is approved (as Vyleesi) to treat hypoactive sexual desire disorder in women. The nickname is slightly imprecise — PT-141 acts on desire through the central nervous system via melanocortin receptors, not on blood flow the way Viagra does — but it captures the intended use.
Can Melanotan 2 be used for libido instead of PT-141?
Melanotan 2 does produce a libido/erectile effect through MC4R, but that is a side effect of a tanning compound. PT-141 is the more targeted option for sexual-function research because it does not carry the tanning and pigmentation effects (darkening moles, etc.) that Melanotan 2 does.
Do both cause tanning?
No. Melanotan 2 activates the pigment receptor (MC1R) and tans; PT-141 does not meaningfully activate MC1R and does not tan. That pigment-receptor activity is the main thing that separates the two cousins.
References
- Research literature on bremelanotide (PT-141) melanocortin MC3/MC4 receptor activity and approval for HSDD.
- Research literature on Melanotan II melanocortin receptor profile (MC1R/MC3R/MC4R) and its combined tanning and libido effects.
Last updated: July 13, 2026
Disclaimer: This information is for educational and research purposes only. Peptides are research chemicals not intended for human consumption. See the PT-141 and Melanotan 2 research pages for reconstitution detail.