Melanotan II: Reference Overview and Reconstitution Notes

Melanotan II is a man-made peptide closely related to a natural hormone that helps control skin pigment. It is grouped with skin and cosmetic research compounds. It is for research only and is not approved by the FDA.

What it is

Melanotan II is a man-made, ring-shaped chain of seven amino acids (the tiny building blocks that make up all proteins). Think of it like a short necklace with seven beads clipped into a circle. It was created in a lab to mimic alpha-melanocyte-stimulating hormone (alpha-MSH), a natural hormone in the body that helps control skin color. It works as an activator at four cell switches known as melanocortin receptors: MC1, MC3, MC4, and MC5. Each switch sits on different types of cells and controls a different function.

Research context and categorization

Primary Research Channels

Melanotan II is most often grouped under the skin and cosmetic category of research peptides. It also overlaps into nerve-and-hormone (neuroendocrine) and reproductive signaling because of the cell switches it activates. It is commonly discussed in relation to melanogenesis, which is the process by which the body makes pigment (color) in the skin. This process runs through the MC1 receptor. Early pilot studies have looked at how the compound affects skin darkening.

Appetite and Sexual-Function Pathways

Because it also activates the MC4 receptor, researchers discuss Melanotan II in relation to appetite and hormone signaling. It is also studied in connection with sexual-function pathways. Observations made during early Melanotan II research led to the separate development of bremelanotide (PT-141), a related compound that was later approved by the FDA for a specific use.

The uses of Melanotan II itself are still under investigation. It has not completed the trials needed for approval. None of the effects described above are confirmed or approved for Melanotan II.

Status

Key point: Melanotan II is an unapproved, investigational substance and is strictly prohibited in sports at all times under the WADA S0 class.

• Regulatory status: Research-only. Melanotan II is not FDA-approved for any use. It is treated as an investigational, unapproved substance.
• Sport status: Prohibited under the WADA Prohibited List. Because it is a peptide without regulatory approval for human therapeutic use, it falls under the non-approved substances class (S0). This class is banned at all times, both in-competition and out-of-competition.

Reconstitution notes (general)

Lyophilized (freeze-dried) peptides are mixed back with bacteriostatic water before use in the lab. Bacteriostatic water is simply water with a small amount of preservative added to slow bacterial growth. The concentration you end up with equals the milligrams of peptide in the vial divided by the milliliters of water added.

For example, 10 mg mixed with 2 mL of bacteriostatic water gives a 5 mg/mL stock solution. A reconstitution calculator is available at peptide calculator.

Dilution and handling notes (compound-specific)

Melanotan II ships as a freeze-dried powder and is one of the more forgiving peptides to reconstitute (mix back into solution).

Recommended Dilutions

• A common starting point for a 10 mg vial is 2 mL of bacteriostatic water, giving a 5 mg/mL stock solution.
• Using more water, such as 3 mL to 4 mL, produces a lower, more dilute stock (roughly 3.3 mg/mL or 2.5 mg/mL). Some researchers prefer this for finer measurement.

Some peptides gel, clump, or resist dissolving when concentrated. Melanotan II is different. It typically dissolves quickly and produces a clear, colorless solution within seconds to about a minute.

Handling Best Practices

1. Direct the water down the inner glass wall of the vial rather than aiming it straight onto the powder cake.
2. Swirl gently rather than shaking or using a vortex mixer. Vigorous agitation adds foam and puts mechanical stress on the compound. That stress can cause it to clump together, a process called aggregation.
3. Protect from light: Melanotan II is sensitive to UV rays and prolonged light exposure. Keep both the sealed powder and the mixed solution away from light at all times.

If the solution turns cloudy or discolored, or shows visible particles, that is a sign of aggregation (clumping), degradation (breakdown), or contamination. Adding more water or filtering will not fix this. Discard the vial.

Handling and storage

Store the reconstituted (mixed) vial in a refrigerator at 2 to 8 degrees C. Keep it away from direct light at all times, both before and after mixing.

Storage Checklist

• Wipe the rubber stopper with an alcohol swab before each draw.
• Label the vial with the date you mixed it so you can track its age.
• Use the reconstituted solution within about a four-week refrigerated window.
• Discard the vial if the contents become cloudy or discolored, or if you see particles floating in it.

Related reading

• MGF (Mechano Growth Factor)
• MK-677 (Ibutamoren)
• MOTS-c
• How Reconstitution Works
• How Long Does a Reconstituted Vial Last?

Tools and supplies

• peptide calculator
• Bacteriostatic Water 30 ml
• Gansulin Metal Reusable Pen
• 3 ml Glass Cartridges (10-pack)
• Complete Starter Kit

Reminder: research and educational reference only. Preppin Peppers sells hardware and materials, not peptides. Not medical, dosing, or health advice, not evaluated by the FDA, and not intended for human or animal use.

Frequently asked questions

What is Melanotan II and how does it work?

Melanotan II is a synthetic 7-amino acid cyclic peptide that mimics alpha-MSH hormone and activates melanocortin receptors MC1, MC3, MC4, and MC5, influencing skin pigmentation and other signaling pathways.

What is the regulatory status of Melanotan II?

Melanotan II is not FDA-approved for any use, classified as an investigational research substance, and is prohibited in sports under WADA S0 class (non-approved substances) at all times, in-competition and out-of-competition.

How do you reconstitute Melanotan II for research?

Add bacteriostatic water to the lyophilized powder - a common starting point is 10mg with 2mL for a 5mg/mL stock solution, or use 3-4mL for more dilute solutions around 2.5-3.3mg/mL.

What the research community gets wrong about Melanotan II

• "It is basically the same as bremelanotide (PT-141)." They are separate compounds. Melanotan II is a cyclic peptide that activates several melanocortin receptors (MC1, MC3, MC4, and MC5), while PT-141 is a distinct molecule studied on its own. Treating vials of one as a stand-in for the other in a protocol will give you the wrong reference data.
• "A ring-shaped peptide is indestructible." The lactam ring does make Melanotan II sturdier than many straight-chain peptides, but it still breaks down. Heat, repeated freeze-thaw, and long storage all degrade the powder and the mixed solution over time.
• "It dissolves easily, so handling does not matter." Easy to dissolve is not the same as hard to damage. Shaking or vortexing forces air into the liquid and adds shear stress, and that mechanical stress can still make peptide molecules clump together (aggregate) even in a compound that goes into solution quickly.
• "Light exposure is not a real concern at the bench." Melanotan II is sensitive to UV and to long light exposure. Leaving the sealed powder or the mixed vial out on an open bench under room lighting is enough to start breaking it down, so keep both shielded from light.
• "A cloudy vial just needs more water or a quick filter." Cloudiness, color change, or floating particles point to aggregation, breakdown, or contamination. Adding water or filtering does not reverse any of those. Log it and discard the vial.

From our bench: If you reconstitute a Melanotan II vial, we would like your real numbers. After adding your bacteriostatic water down the glass wall and swirling gently, time how many seconds it takes to reach a clear, colorless solution, note the vial strength and the water volume you used, and record whether the vial stayed clear across your refrigerated storage window. Share the raw observation, no rounding, and we will add measured data points to this page instead of general estimates.

Sources

1. Bacteriostatic Water for Injection, USP , FDA/DailyMed label (0.9% benzyl alcohol)
2. Duerkop et al., Biotechnol J 2018 , Impact of Cavitation, High Shear Stress and Air/Liquid Interfaces on Protein Aggregation
3. Sigma-Aldrich (Merck) , Handling and Storage Guidelines for Peptides and Proteins
4. PubChem, Melanotan II (Compound CID 92432), molecular formula C50H69N15O9, cyclic melanocortin peptide
5. Van der Poorten et al., CLIPSing Melanotan-II to Discover Multiple Functionally Selective hMCR Agonists, J Med Chem (2022)
6. Wessells et al., Melanocortin receptor agonists, penile erection, and sexual motivation: human studies with Melanotan II, Int J Impot Res (2000)