How much bacteriostatic water do I add to a 40 mg retatrutide vial?

There is no single right amount. More water makes each draw bigger and easier to measure; less water keeps the volume small. With 10 mL, a 40 mg vial is 4 mg/mL, so every 10 units on a U-100 insulin syringe holds 400 mcg. With 2 mL it is 20 mg/mL (2 mg per 10 units). With 3 mL it is 13.33 mg/mL (1.333 mg per 10 units). With 5 mL it is 8 mg/mL (800 mcg per 10 units).

How many units is 2 mg of retatrutide from a 40 mg vial?

With 10 mL of water the vial is 4 mg/mL, so 2 mg is 0.5 mL, or 50 units on a U-100 syringe. With a different water volume the units change but the amount does not. The amount is an example for the math, not a recommendation.

How many 2 mg draws are in a 40 mg retatrutide vial?

20 (40 mg ÷ 2 mg), whatever volume of water you add. In practice a little is lost to the syringe dead space and the last drops in the vial.

Retatrutide 40 mg Reconstitution: BAC Water & Units

Short answer: 10 mL of bacteriostatic water in a 40 mg retatrutide vial makes 4 mg/mL. On a U-100 insulin syringe (1 mL = 100 units), every 10 units then holds 400 mcg. More water gives a weaker solution and a bigger draw for the same amount; the amount in the vial stays 40 mg.

Water volume chart for a 40 mg vial

40 mg retatrutide vial, U-100 insulin syringe.
Water added	Concentration	Per 10 units	Per 1 unit
2 mL	20 mg/mL	2 mg	200 mcg
3 mL	13.33 mg/mL	1.333 mg	133.333 mcg
5 mL	8 mg/mL	800 mcg	80 mcg
10 mL	4 mg/mL	400 mcg	40 mcg

Syringe units by amount

The amounts below are examples to show the conversion, not doses. How much to take is a decision for you and your prescriber.

Units on a U-100 syringe from a 40 mg vial.
Water added	1 mg	2 mg	4 mg
2 mL	5 units	10 units	20 units
3 mL	7.5 units	15 units	30 units
5 mL	12.5 units	25 units	50 units
10 mL	25 units	50 units	100 units

A 40 mg vial holds 40 draws of 1 mg, 20 draws of 2 mg, 10 draws of 4 mg, no matter how much water you add.

How far a 40 mg vial goes

Draws per vial depend only on the amount per draw, not on the water. The volume and units columns use 10 mL of water (4 mg/mL). Example amounts only, not doses.

40 mg vial: draws, volume and units per example amount.
Amount per draw	Draws per vial	Volume per draw	Units per draw
500 mcg	80	0.125 mL	12.5 units
1 mg	40	0.25 mL	25 units
2 mg	20	0.5 mL	50 units
4 mg	10	1 mL	100 units
8 mg	5	2 mL	over 1 mL

Real counts run a little lower: some liquid stays in the syringe and at the bottom of the vial.

40 mg next to other retatrutide vial sizes

To get the same 4 mg/mL from another vial size, scale the water with the vial. Same strength means the same units for the same amount, whichever vial it comes from.

Water for 4 mg/mL, and 2 mg draws per vial, by vial size.
Vial	Water for 4 mg/mL	2 mg draws per vial
5 mg	1.25 mL	2.5
10 mg	2.5 mL	5
15 mg	3.75 mL	7.5
20 mg	5 mL	10
30 mg	7.5 mL	15
40 mg (this page)	10 mL	20
50 mg	12.5 mL (over 10 mL)	25
60 mg	15 mL (over 10 mL)	30

The math

Concentration. 40 mg ÷ 10 mL = 4 mg/mL
Volume to draw. amount ÷ 4 mg/mL = mL
Syringe units. mL × 100 = units

For a different water volume or amount, the free peptide reconstitution calculator works backwards from the amount you want and suggests a water volume that lands on a clean syringe mark.

Other retatrutide vial sizes: Retatrutide 5 mg · Retatrutide 10 mg · Retatrutide 15 mg · Retatrutide 20 mg · Retatrutide 30 mg · Retatrutide 50 mg · Retatrutide 60 mg

Half-life, time to peak and sources are on the main Retatrutide guide.

Retatrutide 40 mg reconstitution: how much water and how many units