RESEARCH MONOGRAPH · KDC-MN-093

Melanotan II

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

61/100

Cyclic broad-spectrum melanocortin agonist with notable libido and tanning effects, plus the dirtiest receptor selectivity profile of the class

Melanotan II is the cyclic heptapeptide MSH analog developed alongside Melanotan I at Arizona by the Hadley and Hruby group, with the lactam bridge cyclization conferring increased stability and potency relative to the linear parent. The key pharmacological difference from Melanotan I is the receptor selectivity profile: MT2 activates MC1R (pigmentation), MC3R, MC4R (libido and erectile function), and MC5R with similar affinity rather than being MC1R-selective. So you get the tanning of MT1 plus the central sexual-function effects that PT-141 was eventually designed to capture selectively.

What we like, narrowly: as a tool compound for studying broad melanocortin receptor pharmacology, MT2 is informative precisely because it hits multiple MC subtypes. The pro-libido effects (mediated through MC3R and MC4R) plus the pigmentation effects (MC1R) plus the satiety effects (MC4R) and the autonomic effects make it a good positive control in melanocortin receptor work even though it's not selective.

What we dont like is everything about the off-label use case. The combination of MC4R activation (nausea, blood pressure changes, hyperpigmentation through MC1R) plus the lack of receptor selectivity means the side effect profile is rougher than either MT1 (more MC1R selective) or PT-141 (better MC4R selective). Hyperpigmentation, melanocyte activation in atypical nevi, gastrointestinal effects, and transient hypertension are all common. The melanoma surveillance concern that applies to MT1 applies more strongly to MT2 because of higher peak MC1R activation per dose and the typical cosmetic-tanning dosing patterns.

Sourcing is mature but variable. The 7-residue cyclic peptide is well-established synthesis and reputable peptide vendors produce HPLC pure material at gram scale. The cyclization step is the main quality control variable; verify mass spec to confirm the lactam bridge. Cheap supplier material can include linear precursor or partial cyclization products.

For research on broad-spectrum melanocortin pharmacology, MT2 is a useful tool. For pretty much anything else, the better-characterized cousins (MT1 for pigmentation research, PT-141 for sexual function research) are cleaner tools. The dirty receptor profile is a feature for some research questions but a problem for translation.

Evidence: 50
Mechanism: 75
Reliability: 65
Safety: 45
Sourcing: 72
Value: 65
Signal: 65
Staying power: 50

Plain-language summary Intrigue 65 / 100

Melanotan II is a cyclic version of melanotan I, more potent and shorter-acting. It produces tanning, libido enhancement, and appetite suppression through different melanocortin receptor subtypes. Used in research and unsanctioned tanning communities. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Cyclic alpha-MSH analog

A cyclic alpha-MSH analog with both skin pigmentation and sexual response effects, sold as a research chemical with significant safety concerns.

Abstract

Melanotan II (MT-II; CAS 121062-08-6; molecular formula C50H69N15O9; molecular weight 1024.18) is a cyclic heptapeptide alpha-MSH analog developed at the University of Arizona in parallel with Melanotan I. The compound shows higher receptor affinity than the linear Melanotan I but with non-selective melanocortin receptor activity (MC1, MC3, MC4, MC5). The clinical effect profile combines the skin pigmentation of MC1 activation with the sexual response effects of MC4 activation; this dual activity led to development of the more selective bremelanotide for sexual function applications and sustained pigmentation via Melanotan I. Melanotan II is not approved by any regulatory authority and is sold as a research chemical with significant safety concerns: the non-selective receptor activity produces reliable adverse events including nausea, flushing, blood pressure elevation, and concerning case reports of melanocyte dysplasia and atypical mole development. The compound should be regarded as substantially more hazardous than the more selective marketed melanocortin agonists.

Mechanism of action

Non-selective cyclic alpha-MSH analog; both pigmentation (MC1) and sexual response (MC4) effects. Higher affinity than Melanotan I.

Reported research dose ranges

0.25 to 1 mg SC reported in the research literature (research-grade); significant safety concerns.

References

Wessells H, et al. Synthetic melanotropic peptide initiates erections in men with psychogenic erectile dysfunction. J Urol 1998.

Read the full monograph

The full reference document covers compound identification, discovery and developmental history, mechanism of action, pharmacokinetics, reported research dose ranges, sourcing and quality verification, reconstitution and handling, stack interaction considerations, and a curated reference list. Available as a research-use-only PDF download.

KDC-MN-093

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

Kodiac sells research compounds for investigative use only.

Melanotan II

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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