How Long Does Melanotan II Last? Storage Before and After Mixing
Lyophilised Melanotan II keeps for a year or more sealed, dry and frozen; once mixed with bacteriostatic water it lasts 8 to 12 weeks at 2 to 8 °C under Vistara Labs’ handling guidance, with quality slowly fading from around week 6 to 8. Supplier data sheets give powder and frozen-stock figures, but no published study gives a refrigerated window for Melanotan II in bacteriostatic water, so that window is the general peptide guidance. Its ring structure and the absence of methionine and cysteine make it one of the sturdier peptides on the shelf, but its tryptophan and histidine still call for dark, cold storage, and a mixed vial is never frozen.
Findings
- Melanotan II is a seven-residue cyclic lactam analogue of alpha-MSH, closed by a bridge between aspartic acid and lysine (Al-Obeidi et al., J Med Chem, 1989).
- A chemical supplier’s data sheet rates the powder at 2 years at −80 °C and 1 year at −20 °C, sealed away from moisture.
- The same sheet gives a stock solution 1 month at −20 °C and 6 months at −80 °C, and lists the sequence as Ac-Nle-Asp-His-D-Phe-Arg-Trp-Lys-NH2, (2→7)-lactam.
- A second supplier rates its acetate salt, stored as a solid at −20 °C, as stable for at least 4 years.
- The sequence has no methionine and no cysteine; tryptophan and histidine are its oxidation-prone residues.
How long does Melanotan II powder last?
The MedChemExpress data sheet gives Melanotan II powder 2 years at −80 °C and 1 year at −20 °C, stored sealed and away from moisture. Cayman Chemical rates its acetate salt at 4 years or more at −20 °C. Moisture is the main enemy of a freeze-dried cake: it lets the same reactions that happen in solution start in the solid. The Melanotan II 10 mg vial is kept capped, boxed, cold and dark, in the fridge for near-term work or the freezer for longer holds, and a cold vial is brought to room temperature before opening so that condensation does not form on the powder.
How long does Melanotan II last after mixing?
At 2 to 8 °C, dark and accessed only through a swabbed stopper, mixed Melanotan II lasts 8 to 12 weeks, with quality fading from around week 6 to 8. That is the general row in how long peptides last after mixing, which lists Melanotan II among the peptides it covers. The Melanotan II reconstitution page has the calculator for the 10 mg vial. Cayman’s sheet advises against keeping its own pH 7.2 buffer solution for more than a day; that is a caution for an unpreserved neutral buffer, not a measured breakdown time for a cold vial mixed with bacteriostatic water.
What the sequence says about stability
Melanotan II is seven residues closed into a ring by a lactam bond between the side chains of aspartic acid and lysine, with an acetylated start and an amidated end. It belongs to a series of cyclic analogues designed from alpha-MSH, and the norleucine at its start sits where alpha-MSH carries a methionine (Al-Obeidi et al., 1989). Norleucine has no sulphur, so it cannot oxidise the way methionine does, and oxidation of methionine is one of the commonest ways peptides change in solution (Manning et al., Pharm Res, 2010). The sequence also has no cysteine, asparagine or glutamine. What remains is a tryptophan, which oxidises, especially under light, and a histidine, which can oxidise too. The practical result is the standard window, with extra attention to light, a tight stopper and gentle swirling rather than shaking.
What the frozen-solution figures mean
The supplier’s 1 month at −20 °C and 6 months at −80 °C apply to stock solutions frozen once and kept sealed, a laboratory practice for single-use aliquots. They are not a reason to freeze a working vial that will be thawed and opened again.
How long does Melanotan II last at room temperature?
There is no published figure for Melanotan II in solution at room temperature. A mixed vial is taken out of the fridge only for handling, because warmth speeds the oxidation reactions above. Haze that appears later in a stored vial points to warm or bright storage.
Can Melanotan II be frozen?
The powder can, and the supplier’s longest figures are freezer figures. Single-use aliquots of solution can be frozen once. A working vial should not be frozen and thawed repeatedly, since freeze-thaw cycles aggregate peptides in solution, and the nasal spray is never frozen.
How can you tell mixed Melanotan II has degraded?
- Yellowing or any tint. Mixed Melanotan II should be clear and colourless.
- Cloudiness that does not clear within 10 to 15 minutes of mixing, or that appears later.
- Particles or sediment.
- Strands, gel or thickening that will not disperse.
Oxidation itself is invisible, which is why the time window applies even to a vial that still looks perfect.
How long does Melanotan II nasal spray last?
The Melanotan II nasal spray arrives ready-mixed in sterile saline in a sealed metered atomiser, so there is nothing to reconstitute. It follows how to store a peptide nasal spray: an opened bottle is kept at 2 to 8 °C, upright and capped, in the main body of the fridge rather than the door, and in the dark in its box. It keeps as long as its label allows; no fixed number of weeks is set for an opened spray. It is never frozen, and for a day away from the fridge an insulated bag with a cold pack keeps it cool.
Travelling with Melanotan II
Sealed powder vials are the form to travel with. A mixed vial travels upright in an insulated case with a cold pack that does not touch the glass, kept out of the light.
Melanotan II storage at a glance
| State | Where | How long |
|---|---|---|
| Powder, sealed | −20 °C / −80 °C, dry | 1 year / 2 years (supplier data sheet); 4 years or more at −20 °C for the acetate salt (second supplier) |
| Powder, sealed | 2 to 8 °C, dark | Near-term holds; no published figure |
| Mixed with bacteriostatic water | 2 to 8 °C, dark | 8 to 12 weeks, fading from week 6 to 8 (store guidance) |
| Solution aliquots, frozen once | −20 °C / −80 °C | 1 month / 6 months (supplier data sheet) |
| Mixed, room temperature | Handling only | No published figure |
Certificates of analysis are on the lab reports page, and every order ships from within Canada by Canada Post Xpresspost.
Vistara Labs supplies Melanotan II as a laboratory research material. The windows on this page describe how long the peptide stays in good condition.
Frequently asked questions
How long does Melanotan II last in the fridge after mixing?
Under Vistara Labs’ handling guidance, 8 to 12 weeks at 2 to 8 °C in the dark, with quality fading from around week 6 to 8.
How long does Melanotan II last at room temperature?
No published figure exists for Melanotan II in solution at room temperature. A mixed vial is kept in the fridge and taken out only for handling.
Can you freeze Melanotan II?
Yes as powder: one supplier rates it at 1 year at −20 °C and 2 years at −80 °C. Solution can be frozen once as single-use aliquots, but a working vial should not go through repeated freeze-thaw cycles, and the nasal spray is never frozen.
Does Melanotan II go bad?
Yes, slowly. Its ring and its lack of methionine help, but its tryptophan and histidine oxidise in solution, faster with warmth and light. Cloudiness, particles, a tint or gel mean it has degraded.
How long does Melanotan II nasal spray last once opened?
As long as its label allows, kept at 2 to 8 °C, upright, capped and in the dark. No fixed number of weeks is set for an opened spray, and the bottle is never frozen.
Handling windows: Vistara Labs, October 2026. Sources: Al-Obeidi F et al. Potent and prolonged acting cyclic lactam analogues of alpha-melanotropin: design based on molecular dynamics. J Med Chem. 1989. PMID 2555512. Manning MC et al. Stability of protein pharmaceuticals: an update. Pharm Res. 2010. PMID 20143256. MedChemExpress. Melanotan (MT)-II, HY-P0267, product data sheet: sequence, solubility and storage. PDF. Cayman Chemical. Melanotan II (acetate), item 27316, product information: storage, stability and solubility. PDF.
More on this: How Long Do Peptides Last After Mixing?
All products supplied by Vistara Labs are intended for laboratory research use only. They are not drugs, are not approved for human or veterinary use, and are not intended to diagnose, treat, cure or prevent any condition. Nothing on this page constitutes medical advice or guidance for use in humans.
