How Much Bacteriostatic Water for a Melanotan II 10 mg Vial?

A 10 mg vial of Melanotan II reconstituted with 2 mL of bacteriostatic water gives a concentration of 5 mg/mL; with 1 mL it gives 10 mg/mL. The calculation depends only on the quantity in the vial and the volume of water added, so the figures below apply to any 10 mg vial.

View product →

There is no single correct volume. Adding more water does not change how much is in the vial. It spreads the same quantity through a larger volume, which changes how many syringe units correspond to a given amount. The tables on this page use volumes that produce round numbers on a U-100 syringe; other volumes work identically as long as the resulting concentration is written on the vial.

Concentration by water volume

Concentration is the quantity in the vial divided by the water volume. A 10 mg vial holds 10 mg whether it receives 1 mL or 5 mL; only the mg/mL figure moves. The right-hand column converts each concentration into the number of U-100 units that contain 1 mg.

Vial	Bacteriostatic water added	Concentration	Units containing 1 mg
10 mg Melanotan II	1 mL	10 mg/mL	10 units
10 mg	2 mL	5 mg/mL	20 units
10 mg	3 mL	3.33 mg/mL	30 units
10 mg	5 mL	2 mg/mL	50 units

Before choosing a larger volume, check that the vial has headspace for it. A 10 mL vial of bacteriostatic water reconstitutes five 10 mg vials at 2 mL each.

Reading the concentration on a U-100 syringe

A U-100 insulin syringe is graduated in units, and 100 units equal 1 mL. Units are therefore millilitres multiplied by 100: 0.1 mL is 10 units and 0.25 mL is 25 units. A 0.5 mL syringe carries 50 units and a 0.3 mL syringe carries 30 units on the same scale, with finer markings that make small volumes easier to read.

To find the volume that contains a given amount, divide the amount by the concentration. At 5 mg/mL (a 10 mg vial with 2 mL of water), the volume that contains 1 mg is 1 divided by 5, which is 0.2 mL, or 20 units. The table below runs the same calculation for four arbitrary amounts. They illustrate the arithmetic and nothing else.

Amount (illustrative)	Volume at 5 mg/mL	U-100 units
0.25 mg	0.05 mL	5 units
0.5 mg	0.1 mL	10 units
1 mg	0.2 mL	20 units
2 mg	0.4 mL	40 units

At 10 mg/mL, which the same vial gives with 1 mL of water, every volume in the table moves in proportion: a 1 mg draw measures 10 units instead of 20. Volumes below about 0.1 mL are hard to read accurately on a 1 mL syringe. Either move to a 0.3 mL or 0.5 mL syringe, or reconstitute with more water so that the same mass occupies a larger, more legible volume.

The Melanotan II vial

Melanotan II is a cyclic heptapeptide analogue of alpha-MSH; the ring is what makes it more stable than the natural hormone. This page covers the 10 mg lyophilised vial. Its metabolite PT-141 is also a 10 mg vial and uses the same tables. Certificates of analysis for the catalogue are published on the Lab Results page. The Melanotan nasal spray is supplied pre-mixed and needs no reconstitution; this page is for the lyophilised vial only.

Melanotan II’s ring is a lactam bridge between an aspartic acid and a lysine, and it is that closed structure that resists the enzymes which break down natural alpha-MSH within minutes. Its clinical history led to PT-141, which became an approved medicine; Melanotan II did not, and it is handled strictly as a research material. The Melanotan II nasal spray is the no-reconstitution alternative, at roughly 28 metered sprays of 350 mcg per 10 mg bottle. The history is in Melanotan II: the clinical history and the PT-141 connection.

Reconstitution technique

Let the vial reach room temperature, swab both stoppers, and run the measured water slowly down the inside wall of the vial rather than onto the powder. Swirl or tilt gently until the cake dissolves, never shake, and give any remaining powder a few minutes to settle into solution. Label the vial with the date and the concentration, then keep it refrigerated at 2 to 8 °C and protected from light. The full method, with the reason behind each step, is in how to reconstitute peptides with bacteriostatic water.

Why the solution should look clear

Properly reconstituted Melanotan II forms a clear, colourless solution. Cloudiness, strands or a gel that will not disperse usually mean the water went in too fast or the vial was shaken; haze that appears later points to warm or bright storage. The causes are covered in why peptides gel or go cloudy.

Bacteriostatic water, not sterile water

Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that allows a refrigerated vial to be accessed more than once; plain sterile water is intended for single access. The difference is explained in bacteriostatic water explained.

Frequently asked questions

How much bacteriostatic water do I add to a 10 mg vial of Melanotan II?

There is no single correct volume. With 2 mL of bacteriostatic water a 10 mg vial of Melanotan II gives 5 mg/mL; with 1 mL it gives 10 mg/mL. Adding more water does not change the quantity in the vial, it spreads it through a larger volume, so write the concentration you chose on the vial.

How many 10 mg vials does a 10 mL vial of bacteriostatic water cover?

A 10 mL vial of bacteriostatic water reconstitutes five 10 mg vials at 2 mL each. Check that the peptide vial has headspace for the volume before choosing a larger one.

How many units on a U-100 syringe contain 1 mg at 5 mg/mL?

At 5 mg/mL (a 10 mg vial with 2 mL of water), the volume that contains 1 mg is 1 divided by 5, which is 0.2 mL, or 20 units. Units are millilitres multiplied by 100, so 0.1 mL is 10 units. The amounts on this page illustrate the arithmetic only.

What should reconstituted Melanotan II look like?

Properly reconstituted Melanotan II forms a clear, colourless solution. Cloudiness, strands or a gel that will not disperse usually mean the water went in too fast or the vial was shaken; haze that appears later points to warm or bright storage. More on the causes in why peptides gel or go cloudy.

Can I use sterile water instead of bacteriostatic water?

Only for a vial that will be accessed once. Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that allows a refrigerated vial to be accessed more than once; plain sterile water is intended for single access. Details in bacteriostatic water explained.

How should a reconstituted Melanotan II vial be stored?

Refrigerated at 2 to 8 °C, protected from light and labelled with the date and the concentration. Unopened lyophilised vials are kept cold and dark until they are needed. The full storage guide is how to store research peptides.

Work it out for a different vial or concentration

Our peptide calculator opens pre-set for a 10 mg vial with 2 mL of water and marks the 1 mg draw of 20 units on a syringe diagram. Change the vial size, water volume, amount or syringe and it recalculates.

Products: Melanotan II 10 mg and bacteriostatic water 10 mL.

Related reading. Melanotan II and PT-141: the clinical history and Canadian buying guide.

References

Melanotan II has direct human research from small controlled studies, centred on pigmentation and erectile function. Adverse effects including nausea were commonly reported.

1. Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical studyDorr RT et al. · Life Sci 1996 · PMID 8637402Placebo-controlled pilot phase 1 study; measurable pigmentation after repeated low-dose exposure. Nausea, fatigue, yawning and spontaneous erections observed.
2. Effect of an alpha-melanocyte stimulating hormone analog on penile erection and sexual desire in men with organic erectile dysfunctionWessells H et al. · Urology 2000 · PMID 11018622Randomised, double-blind, placebo-controlled crossover trial; 10 men with organic erectile dysfunction. Nausea common and sometimes severe.

Links open the study record on PubMed so the source can be checked directly. Listing a study is not a claim that its findings apply to any other use, product or route of administration. Research use only.