> Research Use Only Disclaimer: Melanotan II (MT-II) is not approved by the FDA for human use. All dosing information presented here is derived from published scientific literature and is intended strictly for educational and research reference purposes. This article does not constitute medical advice. Consult a licensed healthcare professional before any use of investigational compounds.
Melanotan II is among the most studied synthetic melanocortin peptides, investigated across three distinct research domains: skin pigmentation biology, sexual function neuropharmacology, and appetite regulation. Despite its high organic search interest and decades of published literature, no standardized clinical dosing protocol exists — the protocols outlined here are derived directly from peer-reviewed clinical studies and represent the parameters used in controlled research contexts.
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What Is Melanotan II (MT-II)?
Melanotan II (MT-II) is a synthetic cyclic heptapeptide analog of alpha-melanocyte-stimulating hormone (α-MSH), developed in the 1980s and 1990s at the University of Arizona by Mac Hadley, Victor Hruby, and colleagues. The research goal was to create a potent, metabolically stable melanotropin that could induce melanogenesis without requiring UV radiation exposure — originally conceived as a photoprotective intervention in fair-skinned individuals at high risk of skin cancer.
Molecular structure: Ac-Nle-c[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂ (cyclic heptapeptide)
Molecular weight: 1024.2 Da
CAS number: 121062-08-6
Receptor binding: MC1R, MC3R, MC4R, MC5R (non-selective agonist)
The cyclization strategy — replacing the linear α-MSH sequence with a lactam-bridged cyclic core — dramatically increased both receptor binding affinity and resistance to enzymatic degradation. MT-II binds MC1R with approximately 1,000× greater potency than native α-MSH, a pharmacodynamic advantage that explains its low dosing thresholds in research settings.
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MT-II vs. Melanotan I: Key Structural and Pharmacological Differences
Understanding the differences between Melanotan I and Melanotan II is essential for interpreting the dosage literature, as their receptor selectivity profiles produce substantially different research outcome profiles.
| Property | Melanotan I (Afamelanotide) | Melanotan II |
|---|---|---|
| Structure | Linear 13-aa α-MSH analog | Cyclic 7-aa heptapeptide |
| Primary receptor | MC1R (selective) | MC1R, MC3R, MC4R, MC5R (non-selective) |
| Pigmentation potency | High (FDA-approved via Scenesse implant) | High |
| Sexual function effects | Minimal (MC4R selectivity low) | Prominent (MC4R agonism) |
| Erection research | Not studied | Landmark clinical data (PMID 9679884) |
| Appetite suppression | Minimal | Documented in multiple studies |
| Approved status | FDA-approved (EPP via Scenesse) | No regulatory approval |
| Half-life | ~2.5 hours (linear analog) | ~1.5–2 hours (cyclic) |
MT-I (afamelanotide) selectivity for MC1R makes it the preferred choice for pure pigmentation research with minimal off-target effects. MT-II's broader receptor engagement produces more diverse pharmacology — which is simultaneously its most studied advantage (for MC4R sexual function research) and its primary source of side effects.
See our full Melanotan I vs Melanotan II comparison guide and the Melanotan I Dosage Protocol Guide for detailed afamelanotide reconstitution protocols.
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Melanocortin Receptor Biology: Why MT-II Produces Multiple Effects
MT-II's multi-receptor binding profile is the pharmacological foundation of all its documented research applications. Each receptor subtype sits in different tissues and controls different physiological systems:
MC1R (Melanocortin 1 Receptor)
Located on melanocytes in the skin. MC1R activation triggers the switch from pheomelanin (reddish-yellow pigment) to eumelanin (brown-black pigment), increases melanin synthesis via cAMP-PKA-MITF signaling cascade, and stimulates melanocyte dendritic branching and melanosome transfer to keratinocytes. This is the primary pathway underlying MT-II's tanning and photoprotective research applications.
MC3R (Melanocortin 3 Receptor)
Located in the hypothalamus, limbic system, and peripheral tissues including the heart, gut, and gonads. MC3R participates in energy homeostasis, feeding behavior, and the central regulation of reproductive function. MC3R agonism contributes to MT-II's appetite-suppressive properties observed in clinical studies.
MC4R (Melanocortin 4 Receptor)
The receptor of greatest pharmacological interest for sexual function research. MC4R is expressed in the hypothalamus (paraventricular nucleus), brainstem, and spinal cord pathways that regulate penile erection and sexual arousal. MT-II's agonism at MC4R was the direct precursor to the development of bremelanotide (PT-141/Vyleesi), the first FDA-approved melanocortin drug for hypoactive sexual desire disorder.
MC5R (Melanocortin 5 Receptor)
Present in exocrine glands (sebaceous, lacrimal, salivary). MC5R agonism contributes to sebum production changes and glandular secretion effects — less studied but implicated in some of MT-II's dermatological side effects.
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Reconstitution Protocol: 10mg Vials (Standard Research Format)
MT-II is supplied as a lyophilized (freeze-dried) powder requiring reconstitution before administration. The standard research vial is 10 mg. Bacteriostatic water (BAC water — water with 0.9% benzyl alcohol) is the standard reconstitution solvent for research peptides; it prevents bacterial growth and extends the usability window of reconstituted solutions.
> For research purposes only. Not for human use.
Materials Required
- •MT-II lyophilized vial (10 mg)
- •Bacteriostatic water (BAC water)
- •Sterile insulin syringes (1 mL, 29–31G needle)
- •Alcohol swabs (70% isopropyl)
Step-by-Step Reconstitution
1. Allow both the MT-II vial and BAC water vial to reach room temperature (approximately 30 minutes).
2. Wipe the rubber stopper of both vials with an alcohol swab. Allow to air-dry for 60 seconds before puncturing.
3. Draw up the desired volume of BAC water using a sterile syringe. The volume determines the final concentration (see table below).
4. Insert the needle at a 45° angle into the MT-II vial and inject the BAC water slowly down the inner wall of the vial — do not inject directly onto the lyophilized cake, as this disrupts peptide integrity.
5. Gently swirl the vial until the powder fully dissolves. Do not shake or vortex — this can cause peptide aggregation.
6. Once dissolved, the solution should be clear or very slightly yellow-tinted. Discard if particulate matter is visible or if the solution is opaque.
Concentration Reference Table (10 mg vial)
| BAC Water Added | Final Concentration | Volume per 250 mcg dose | Volume per 500 mcg dose |
|---|---|---|---|
| 1 mL | 10,000 mcg/mL (10 mg/mL) | 0.025 mL (2.5 IU) | 0.05 mL (5 IU) |
| 2 mL | 5,000 mcg/mL (5 mg/mL) | 0.05 mL (5 IU) | 0.1 mL (10 IU) |
| 2.5 mL | 4,000 mcg/mL (4 mg/mL) | 0.0625 mL (~6 IU) | 0.125 mL (~12.5 IU) |
| 5 mL | 2,000 mcg/mL (2 mg/mL) | 0.125 mL (12.5 IU) | 0.25 mL (25 IU) |
| 10 mL | 1,000 mcg/mL (1 mg/mL) | 0.25 mL (25 IU) | 0.5 mL (50 IU) |
Note: IU measurements reference standard U-100 insulin syringe markings where 100 IU = 1 mL.
Practical recommendation for research use: Adding 2 mL BAC water to a 10 mg vial yields 5 mg/mL — a commonly used research concentration that allows for straightforward volume calculations and minimizes measurement error at lower research doses.
For peptide reconstitution calculators, see the Peptides.SO reconstitution tool.
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Research Dosing Ranges: Pigmentation Studies
The following dosing parameters are derived from published research literature. They do not represent clinical recommendations.
Original Phase I Clinical Study (Hadley Lab, University of Arizona)
The foundational pharmacokinetic study of MT-II administered it to 3 healthy male volunteers in a single-blind, placebo-controlled design (Dorr et al., 1996 — PMID 8637402). Subcutaneous injections were administered daily (Monday–Friday) for two consecutive weeks.
Dose escalation protocol used in this study:
- •Starting dose: 0.01 mg/kg/day (approximately 0.7–0.8 mg for a 75 kg subject)
- •Escalation increment: 0.005 mg/kg per step
- •Maximum studied: 0.03 mg/kg/day
- •Identified optimal research dose: 0.025 mg/kg/day (approximately 1.6–2.0 mg for most adult subjects)
Significant melanogenesis (visible skin darkening) was observed at doses ≥0.02 mg/kg, with progression over the two-week treatment window. The investigators noted continued tanning effects for several weeks post-treatment, consistent with the extended half-life of eumelanin in skin.
Community Research Protocol (Loading/Maintenance Model)
In preclinical and community-derived research frameworks, MT-II tanning protocols are structured around a loading/maintenance architecture:
Loading Phase (Weeks 1–4):
- •Starting dose: 100–250 mcg/day (to assess nausea tolerance)
- •Titration target: 500–1,000 mcg/day
- •Administration: subcutaneous injection
- •UV exposure: 10–20 min natural or artificial UV co-stimulation recommended to activate MC1R-primed melanocytes
Maintenance Phase (after desired pigmentation achieved):
- •250–500 mcg, 1–2× per week
- •Continue UV exposure co-stimulation
- •Pigmentation typically persists 4–8 weeks after cessation if UV exposure is maintained
Fitzpatrick Skin Type Dosing Adjustments
Research participants with lower Fitzpatrick scores (I–II: very fair to fair skin) typically require longer loading phases and higher cumulative doses to achieve equivalent pigmentation responses compared to Fitzpatrick III–IV participants, reflecting baseline MC1R expression differences and melanocyte density variation.
| Fitzpatrick Type | Loading Duration | Target Loading Dose | Expected Response Timeline |
|---|---|---|---|
| Type I (very fair, always burns) | 6–8 weeks | 500–1,000 mcg/day | Slow; requires high cumulative dose |
| Type II (fair, usually burns) | 4–6 weeks | 500 mcg/day | Moderate; noticeable by week 3–4 |
| Type III (medium, sometimes burns) | 2–4 weeks | 250–500 mcg/day | Good response; visible by week 2 |
| Type IV (olive, rarely burns) | 1–2 weeks | 100–250 mcg/day | Rapid; maintenance phase sufficient |
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MC4R Research: Sexual Function and Erectile Response Studies
The most clinically significant research application of MT-II beyond pigmentation is its role in elucidating MC4R-mediated sexual function pathways. Two landmark double-blind, placebo-controlled crossover studies established MT-II as a potent erectogenic agent:
Landmark Study 1: Psychogenic Erectile Dysfunction (Wessells et al., 1998)
Design: 10 men with psychogenic erectile dysfunction received MT-II (0.025 mg/kg) or placebo subcutaneously. Penile rigidity was monitored for 6 hours via RigiScan.
Results:
- •8 of 10 MT-II-treated subjects developed clinically significant erections (vs. 0/10 placebo)
- •Mean tip rigidity >80%: 38.0 minutes with MT-II vs. 3.0 minutes with placebo (p=0.0045)
- •Onset: approximately 10–20 minutes post-injection
- •Erection duration: approximately 2.5 hours
- •Conclusion: MT-II is a "potent initiator of erections" in psychogenic ED
(PMID: 9679884 — Journal of Urology, 1998)
Landmark Study 2: Expanded ED Cohort (Wessells et al., 2000)
Design: 20 men with both psychogenic AND organic erectile dysfunction. Same blinded subcutaneous injection protocol.
Results:
- •17 of 20 men developed penile erections with MT-II vs. placebo
- •Mean rigidity duration: 41 minutes at ≥80% tip rigidity
- •Increased sexual desire reported after 68% of MT-II doses vs. 19% of placebo doses (P<0.01)
- •Conclusion: MT-II produced erectogenic response even in organogenic ED — demonstrating central (not just psychogenic) mechanism
(International Journal of Impotence Research, 2000)
Bremelanotide (PT-141) as MT-II Derivative
These MC4R findings directly led to the development of bremelanotide (PT-141), an acid-stable derivative of MT-II that selectively targets MC1R and MC4R. PT-141 received FDA approval in 2019 as Vyleesi for hypoactive sexual desire disorder (HSDD) in premenopausal women — validating the central melanocortin pathway as a legitimate sexual health target. Bremelanotide is now an allowed reference compound in melanocortin receptor research.
Research Dosing for MC4R Sexual Function Studies
The dose established as the standard for MC4R sexual function research is:
- •0.025 mg/kg subcutaneous (approximately 1.5–2.0 mg for most adult subjects)
- •Administered 30–60 minutes before observation window
- •Single-dose paradigm used in both major clinical trials
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Administration Routes: Subcutaneous vs. Nasal Spray
All published clinical trials of MT-II used subcutaneous injection. Nasal spray formulations exist in research markets but lack validated pharmacokinetic data from peer-reviewed trials.
| Route | Estimated Bioavailability | Dose Equivalence | Research Notes |
|---|---|---|---|
| Subcutaneous injection | ~90–100% | Reference | All clinical trials use this route |
| Nasal spray (intranasal) | ~10–40% (variable) | 2.5–10× higher dose needed | No published PK data from peer-reviewed trials |
| Oral | <2% | Not viable | Destroyed by GI proteases |
| Intramuscular (IM) | ~90% | Similar to SQ | Rarely used in published research |
Subcutaneous injection remains the gold standard for MT-II research because:
1. It matches the dosing in all peer-reviewed clinical literature
2. Bioavailability is consistent and near-complete
3. Onset is predictable (10–20 min for MC4R effects)
4. Dose accuracy is maximized
Intranasal administration is an active area of research interest for nasal mucosal absorption studies and comparative bioavailability work. However, the substantially lower and more variable systemic delivery (~10–40% of the injected dose equivalent) means results from intranasal protocols are not directly comparable to the published subcutaneous clinical literature.
Oral bioavailability is negligible (<2%) due to proteolytic degradation in the GI tract. MT-II is not absorbed intact when taken orally.
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Side Effects Profile from Published Literature
MT-II's non-selective melanocortin receptor agonism produces predictable off-target effects. The following profile is compiled from the Hadley Phase I study, the Wessells ED trials, and subsequent pharmacology literature:
Most Common (>50% of subjects in published trials)
Nausea — The most consistently reported side effect. Present in approximately 80–90% of subjects at doses ≥0.025 mg/kg. Typically begins 30–60 minutes post-injection, peaks at 2–4 hours, and resolves within 4–6 hours. Severity is dose-dependent; the 100–250 mcg titration strategy is used in research protocols to assess individual nausea threshold before advancing to higher doses. Mechanism: likely MC3R agonism in the area postrema (brainstem vomiting center) and peripheral gut MC3R/MC4R activation.
Spontaneous Erections — Reported as an intended pharmacodynamic effect in sexual function studies but occurs in pigmentation research protocols as well, given that the dose range overlaps. In the Wessells 1998 study, spontaneous erections were documented at 0.025 mg/kg. Mechanism: MC4R in the paraventricular nucleus of the hypothalamus.
Facial Flushing — Vasodilatory effect, typically appearing within 30–60 minutes of injection and lasting 1–2 hours. Mechanism: MC1R on vascular endothelium and MC3R/MC5R-mediated nitric oxide release.
Less Common
Appetite Suppression — Significant appetite reduction reported in a subset of subjects, attributed to MC3R/MC4R hypothalamic satiety signaling. Exceeds 50% reduction in appetite during loading phase in some community reports, though controlled clinical documentation is less robust.
Stretching and Yawning — Reported as a transient side effect in both the Dorr 1996 and Wessells 1998/2000 studies. Mechanism unclear; possible hypothalamic arousal pathway.
Darkening of Existing Moles and Freckles — MC1R activation on existing melanocytic nevi may accelerate pigmentation in pre-existing lesions. Long-term dermatological monitoring is recommended in research contexts. New or rapidly darkening moles warrant dermatological evaluation.
Dose-Dependent Relationship
| Dose Level | Primary Effects | Side Effect Intensity |
|---|---|---|
| 100 mcg | Minimal MC1R priming | Minimal nausea (tolerance assessment dose) |
| 250 mcg | Mild pigmentation stimulus | Low nausea in most subjects |
| 500 mcg | Significant pigmentation stimulus; MC4R effects begin | Moderate nausea; flushing likely |
| 1,000 mcg (1 mg) | High pigmentation stimulus; strong MC4R activation | High nausea; spontaneous erection likely |
| 0.025 mg/kg (~1.5–2 mg for 70 kg) | Clinical trial dose; full receptor engagement | Nausea in ~80% of subjects |
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Storage and Stability
Lyophilized (Unreconstituted) MT-II
- •Storage: −20°C to −80°C (freezer)
- •Shelf life: 24–36 months when stored correctly
- •Light sensitivity: Store in opaque vial or wrapped in foil; MT-II is photosensitive
Reconstituted MT-II (in Bacteriostatic Water)
- •Storage: 2–8°C (standard refrigerator temperature; do NOT freeze after reconstitution)
- •Stability window: 4–6 weeks when stored refrigerated and protected from light
- •BAC water's 0.9% benzyl alcohol preservative is essential for extending the multi-use vial window; sterile water for injection lacks this protection and reduces stability to ~5–7 days
- •Visible degradation indicators: cloudiness, precipitate, or off-color solution — discard if any present
Temperature cycling (repeated freeze-thaw) significantly degrades cyclic peptides. Reconstituted MT-II should be kept continuously refrigerated and not frozen again after reconstitution.
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MT-II Research Profile: Overview Table
| Parameter | Value/Range |
|---|---|
| Molecular weight | 1024.2 Da |
| Standard vial size | 10 mg (lyophilized) |
| Recommended reconstitution volume | 2 mL BAC water per 10 mg vial |
| Resulting concentration | 5 mg/mL (5,000 mcg/mL) |
| Phase I research dose | 0.025 mg/kg subcutaneous |
| Loading dose range (community protocols) | 250–1,000 mcg/day |
| Maintenance dose range | 250–500 mcg, 1–2× weekly |
| MC4R sexual function research dose | 0.025 mg/kg (single dose) |
| Route (validated by clinical data) | Subcutaneous injection |
| Onset of MC4R effects | 10–20 minutes |
| Duration of MC4R effects | ~2.5 hours |
| Reconstituted stability | 4–6 weeks at 2–8°C |
| Freeze-thaw cycles | Avoid (degrades cyclic peptide) |
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Internal Links and Related Research
For deeper coverage of the Melanotan peptide family:
- •Melanotan II Research Profile — Complete mechanistic overview of MT-II, receptor binding pharmacology, and research history
- •Melanotan I vs Melanotan II Comparison — Side-by-side comparison of receptor selectivity, clinical data, and research applications
- •Melanotan I Dosage Protocol Guide — Afamelanotide (Scenesse) dosing for EPP and pigmentation research
- •Reconstitution Calculator — Interactive tool for calculating peptide concentrations from vial size and solvent volume
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Summary
Melanotan II is one of the most thoroughly researched synthetic melanocortin peptides, with a published literature spanning three decades and two distinct research domains. At the University of Arizona's established research dose of 0.025 mg/kg subcutaneous, MT-II produces reliable melanogenesis through MC1R and significant erectogenic responses through MC4R — effects that have been replicated in multiple double-blind, placebo-controlled crossover studies.
For research reconstitution, adding 2 mL of bacteriostatic water to a 10 mg vial yields a 5 mg/mL solution suitable for precise small-volume dosing. Reconstituted peptide remains stable for 4–6 weeks at 2–8°C when protected from light and thermal cycling.
The non-selective receptor profile of MT-II — particularly its combined MC1R/MC3R/MC4R agonism — distinguishes it from its more selective descendant afamelanotide (Melanotan I) and its MC4R-focused derivative bremelanotide (PT-141). This broad receptor engagement makes MT-II particularly valuable as a pharmacological tool for dissecting melanocortin pathway biology across multiple physiological systems.
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> For research purposes only. Not for human use. This article is intended for educational reference and does not constitute medical advice. Melanotan II is not approved by the FDA or any regulatory body for therapeutic use in humans. Researchers should comply with all applicable institutional review board (IRB) and regulatory requirements when working with investigational peptide compounds.
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Sources: Dorr RT et al. (1996) PMID 8637402 — Phase I clinical evaluation of MT-II; Wessells H et al. (1998) PMID 9679884 — Double-blind placebo-controlled crossover study in psychogenic ED; Wessells H et al. (2000) — International Journal of Impotence Research, expanded ED cohort; Giuliano F (2004) — Journal of Andrology, melanocortin control of penile erection.