How many units is a 1 mg PT-141 dose?

With a 10 mg PT-141 vial reconstituted in 2 mL of bacteriostatic water (5000 mcg/mL), a 1 mg (1000 mcg) dose works out to 1000 divided by 50 mcg per unit, which is 20 units on a U-100 insulin syringe.

How much bacteriostatic water goes into a 10 mg PT-141 vial?

It depends on the concentration you want. A common reference point is 2 mL, which gives 5000 mcg/mL and keeps typical research doses in a readable unit range. Use the calculator to test other volumes and find one that lands your dose on a round syringe mark.

Does a PT-141 dosage calculator handle both mg and mcg?

Yes. Vial labels are almost always in milligrams while research doses are often described in fractions of a milligram or in micrograms. 1 mg equals 1000 mcg, and the calculator converts between the two automatically once a vial size, water volume, and target dose are entered.

PT-141 Dosage Calculator: Reconstitution & Syringe Units

Q: Is PT-141 FDA-approved?

In one specific form, yes. The FDA approved bremelanotide, branded as Vyleesi, in 2019 as a fixed-dose 1.75 mg subcutaneous injection for acquired, generalized hypoactive sexual desire disorder in premenopausal women. The lyophilized research vials sold as PT-141 for reconstitution are a different product and are not FDA-approved for any use.

By PeptCalc Research — Medically reviewed by David Mansour, MD — Last reviewed August 10, 2026

PT-141 vials are labeled in milligrams, while research doses are usually described in micrograms or fractions of a milligram — the exact conversion a PT-141 dosage calculator is built to handle. This is a reference for the arithmetic behind that vial: how vial size and bacteriostatic water volume set concentration, and how concentration turns a target dose into an exact draw on a U-100 insulin syringe. It is written for research purposes only and is not medical advice.

What the calculator does

A PT-141 dosage calculator only needs three numbers to do its job: vial size, water volume, and target dose. The peptide dosage calculator handles the conversion in two directions:

Forward mode — enter vial size, water volume, and target dose, and it returns the syringe units to draw.
Reverse mode — enter vial size, target dose, and a desired unit count, and it returns the water volume that produces it.

Both modes run on the same formula: concentration equals mass divided by water volume, and units equal that volume in mL multiplied by 100 on a U-100 syringe. That formula doesn't change because the vial holds PT-141 instead of another peptide — only the vial's own mass and water volume matter.

PT-141 at a glance

PT-141 is the research name for bremelanotide, a synthetic peptide that acts on melanocortin receptors. It is chemically related to Melanotan II, another melanocortin agonist studied for tanning, but the two are used in different research contexts and the reconstitution numbers for one don't transfer to the other — see the Melanotan II dosage calculator for how that peptide's math compares.

Bremelanotide does have one FDA-approved formulation. Vyleesi is a fixed-dose 1.75 mg subcutaneous injection, approved in 2019 for acquired, generalized hypoactive sexual desire disorder in premenopausal women, administered as a single dose at least 45 minutes before anticipated sexual activity (FDA prescribing information, via DailyMed). That approval covers one specific branded product at one fixed dose. The lyophilized research vials this calculator is built around are a different product, not FDA-approved for any use, and none of the numbers below describe a use recommendation. They describe reconstitution arithmetic, which is identical regardless of a compound's regulatory status.

Typical research concentration

PT-141 most commonly reaches researchers as lyophilized powder in vials in the 5 mg to 20 mg range. Reconstituted in 2 mL of bacteriostatic water, a reference point chosen because it keeps typical research doses on readable syringe marks:

Vial size	Water added	Concentration
5 mg	2 mL	2.5 mg/mL (2500 mcg/mL)
10 mg	2 mL	5 mg/mL (5000 mcg/mL)
20 mg	2 mL	10 mg/mL (10000 mcg/mL)

These are reference points, not requirements — the peptide dosage calculator recalculates concentration for any vial size and water volume actually on hand.

The math

Step 1: Calculate concentration

Concentration = vial mass ÷ water volume

10 mg vial + 2 mL water = 10 ÷ 2 = 5 mg/mL (5000 mcg/mL)

Step 2: Convert concentration to mcg per unit

A U-100 insulin syringe divides 1 mL into 100 units, so:

mcg per unit = concentration (mcg/mL) ÷ 100

5000 mcg/mL ÷ 100 = 50 mcg per unit

Step 3: Convert the target dose to units

Units = target dose (mcg) ÷ mcg per unit

Worked example. A 10 mg PT-141 vial reconstituted in 2 mL of bacteriostatic water is 5000 mcg/mL, which is 50 mcg per unit. The FDA-approved Vyleesi dose of 1.75 mg (1750 mcg) works out to 1750 ÷ 50 = 35 units at that concentration — useful only as a reference point for scale, since the approved product ships as a fixed-dose autoinjector, not a reconstituted vial. A 1 mg (1000 mcg) research reference dose from the same vial is 1000 ÷ 50 = 20 units.

Compare that to a 5 mg vial in the same 2 mL of water: 5 ÷ 2 = 2.5 mg/mL, or 2500 mcg/mL, which is 25 mcg per unit. That same 1 mg dose is now 1000 ÷ 25 = 40 units — a larger draw from a lower-concentration vial, even though the dose in mg hasn't changed at all.

Choosing a water volume

Water volume is the lever that sets how large a given dose reads on the syringe. For a 10 mg vial and a 1 mg (1000 mcg) dose:

Water added	Concentration	mcg per unit	Units for 1000 mcg
1 mL	10000 mcg/mL	100 mcg/unit	10 units
2 mL	5000 mcg/mL	50 mcg/unit	20 units
4 mL	2500 mcg/mL	25 mcg/unit	40 units

None of these rows is more correct than another — 1000 mcg is 1000 mcg regardless of which row it comes from. A larger draw is generally easier to measure precisely on a U-100 barrel than a very small one, since a one-unit misread is a bigger proportional error at the low end. Reverse mode on the peptide reconstitution calculator finds the water volume that lands a specific dose on a round unit mark.

Reconstitution process

Gather the PT-141 vial, bacteriostatic water, a U-100 insulin syringe, and alcohol swabs.
Swab both vial stoppers with alcohol.
Draw the water volume the chosen concentration calls for.
Inject it slowly down the inside wall of the vial, not directly onto the powder.
Swirl gently until fully dissolved — don't shake.
Confirm the resulting concentration matches what was entered into the calculator before drawing a dose.

For the general mixing walkthrough that applies to any peptide vial, see how to reconstitute peptides.

Storage

Reconstituted PT-141 is generally kept refrigerated and protected from light. Unreconstituted lyophilized powder is far more stable than the mixed solution, which is why vials ship dry. Track the date each vial was reconstituted, particularly if more than one vial is in use at different concentrations.

Common mistakes

Confusing mg and mcg. PT-141 vial labels are in milligrams; research doses are often described in fractions of a milligram or in micrograms. 1 mg equals 1000 mcg, and misreading one for the other produces a 1000x error.
Confusing PT-141 with Melanotan II. Both are melanocortin-receptor peptides studied from a shared research lineage, but they're examined for different purposes, and the reconstitution reference numbers for one don't carry over to the other. See the Melanotan II dosage calculator.
Treating the FDA-approved dose as a research reference. Vyleesi's 1.75 mg fixed dose applies to one specific approved autoinjector product, not to a reconstituted research vial at an arbitrary concentration.
Reusing a unit count across a different water volume. As the table above shows, 1000 mcg is 20 units at one concentration and 40 units at another. A unit count only means something relative to the specific concentration it was calculated from.
Using a syringe that isn't U-100. Every unit conversion here assumes 100 units equal 1 mL. A different syringe scale changes the math entirely.

Used as a PT-141 dosage calculator, the peptide dosage calculator skips the arithmetic and returns exact syringe units, with reverse mode available for finding a water volume that lands a dose on a clean mark. For the melanocortin peptide PT-141 is most often confused with, see the Melanotan II dosage calculator. For the general reconstitution process, see how to reconstitute peptides.