PT-141 vs Melanotan 2: One Origin, Two Directions

PT-141 and Melanotan 2 (MT-2) are close relatives. Both are lab-made versions of alpha-MSH, the hormone that darkens skin, and both switch on melanocortin receptors. **MT-2 came first, as a tanning compound, and in its first human study the volunteers also had spontaneous erections (Dorr, 1996). PT-141 was developed from MT-2 to study that second effect. As bremelanotide, it is now approved in the US for low sexual desire in women (Dhillon, 2019).**

The Short Answer

• Melanotan 2 (MT-2) is seven amino acids with a ring, built on the active core of alpha-MSH. In a small first human study, it darkened skin and also caused spontaneous erections, with mild nausea and yawning (Dorr, 1996).
• PT-141 (bremelanotide) is almost the same molecule. It differs from MT-2 at one end only: a free acid where MT-2 has an amide. In two Phase 3 trials with 1,267 premenopausal women, it raised sexual desire and lowered the distress around it (Kingsberg, 2019).
• MT-2 is the tool for pigment research. PT-141 is the tool for research on desire.

How Each One Works

Melanocortin receptors are a family of five. MC1R, in the skin's pigment cells, drives tanning. Receptors in the brain, MC3R and MC4R, are linked to appetite and to sexual behavior. Both peptides reach several of these receptors; what differs is how each has been studied and used.

Melanotan 2

MT-2 was made as a "superpotent" version of alpha-MSH. In its first human study, three men received it on alternating weekdays over two weeks, with salt water on the other days. Two of them had darker skin on the face, upper body and buttocks a week after the last administration. Mild nausea came up at most of the levels tested, and a stretching-and-yawning reflex came with spontaneous erections, on and off for 1 to 5 hours (Dorr, 1996).

A follow-up study tested that second effect in 10 men with erectile problems of psychological origin. MT-2 led to erections in 8 of them. Side effects were nausea, stretching and yawning, and less appetite (Wessells, 1998). For more, see the Melanotan 2 guide.

PT-141

PT-141 acts on melanocortin receptors in the brain. In female rats, it increased the animals' active approaches to a partner without changing reflexes such as lordosis, a sign of an effect on desire rather than on the body's mechanics (Pfaus, 2004).

In people, the two Phase 3 trials found more nausea, flushing and headache than placebo, each in 10% or more of women (Kingsberg, 2019). For more, see the PT-141 guide.

Side-by-Side Comparison

Which One Fits Which Research Question?

Choose MT-2 when your question is about skin pigment: melanin, MC1R signaling, or how skin darkens and how long it lasts.

Choose PT-141 when your question is about desire and arousal, and the brain's melanocortin system. It has the larger human dataset by far, from the Phase 3 trials.

Study both when you want to compare how two nearly identical molecules have been studied for different effects.

Both come as ten-vial kits: PT-141 and Melanotan 2, each 10 mg.

Handling Differences

Both arrive as freeze-dried powder and mix with bacteriostatic water. They are nearly the same size, so the math is the same for both. Label them clearly, since the names give no hint that they are related. Keep mixed vials in the fridge. See how to reconstitute research peptides.

Frequently Asked Questions

Is PT-141 the same as Melanotan 2?

Almost. PT-141 was developed from MT-2 and shares its ring structure. The only change is at one end: PT-141 has a free acid where MT-2 has an amide. The two have been studied for different effects.

Does PT-141 darken the skin like MT-2?

It can. Across the bremelanotide trials, darker skin patches were rare at the approved schedule, but appeared in more than a third of people after up to 16 days in a row of daily use (Clayton, 2022). MT-2 is the one studied for tanning.

Which one is an approved medicine?

PT-141, as bremelanotide (Vyleesi), is approved in the US for acquired low sexual desire in premenopausal women. MT-2 is not approved.

What side effects were seen in the studies?

For MT-2, nausea, a stretching-and-yawning reflex and less appetite. For PT-141, nausea, flushing and headache, each in 10% or more of women in the Phase 3 trials.

Why does MT-2 affect arousal?

It reaches the brain's melanocortin receptors as well as the skin's. The effect showed up in its first human study, and that finding led to PT-141.

Studies Cited

• Dorr RT, et al. (1996). Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Life Sciences.
• Wessells H, et al. (1998). Synthetic melanotropic peptide initiates erections in men with psychogenic erectile dysfunction: double-blind, placebo controlled crossover study. Journal of Urology.
• Pfaus JG, et al. (2004). Selective facilitation of sexual solicitation in the female rat by a melanocortin receptor agonist. Proceedings of the National Academy of Sciences.
• Kingsberg SA, et al. (2019). Bremelanotide for the treatment of hypoactive sexual desire disorder: two randomized phase 3 trials. Obstetrics and Gynecology.
• Dhillon S, Keam SJ (2019). Bremelanotide: first approval. Drugs.
• Clayton AH, et al. (2022). Safety profile of bremelanotide across the clinical development program. Journal of Women's Health.