How do I reconstitute 20mg of retatrutide injection?

The method is the same as for any lyophilized peptide: bring the vial to room temperature, wipe both stoppers with alcohol, draw your planned volume of bacteriostatic water into a U-100 insulin syringe, inject it slowly down the inside glass wall, and swirl until clear. The part specific to a 20mg vial is the arithmetic that follows. 20mg into 1 mL gives 20 mg per mL, so one insulin unit holds 0.2 mg. 20mg into 2 mL gives 10 mg per mL, so one unit holds 0.1 mg. 20mg into 3 mL gives about 6.67 mg per mL, so one unit holds about 0.067 mg. Peptara Labs defaults to 2 mL. The volume changes the unit count, never the amount of peptide in the vial.

How much BAC water do I mix with my peptide?

It depends on the vial strength and on how large you want the unit count to be, because the volume sets the concentration and nothing else. The formula is units = (amount in mg / vial strength in mg) x (bac water in mL x 100). More water means each unit carries less peptide, so the same amount becomes more units on the syringe, which is easier to read accurately. Less water means smaller draws. Two practical limits: the vial has to physically hold the volume you plan to add, and a single 1 mL U-100 syringe only holds 100 units, so very dilute mixes can push one draw past what a syringe can take. Peptara Labs defaults to 2 mL for the 20mg retatrutide vial.

How do I properly reconstitute peptides?

Five things separate a clean reconstitution from a ruined vial. Let the vial reach room temperature first. Wipe both rubber stoppers with a fresh alcohol swab and let them dry. Run the bacteriostatic water down the inside of the glass rather than straight onto the powder. Swirl or roll the vial instead of shaking it, because shaking foams the solution and can fragment the peptide. Then refrigerate at 2 to 8 Celsius and write the volume you used on the label. Our general method page covers the same procedure for every compound in the catalog.

What is bacteriostatic water and can I use something else?

Bacteriostatic water for injection is sterile water containing 0.9 percent benzyl alcohol as a preservative, and it is the standard diluent for multi-use peptide vials. The preservative is the reason a vial can be entered more than once: it inhibits bacterial growth in the vial between draws. Sterile water for injection is a different product and does not carry that preservative. The two vials look alike, so read the label rather than assuming which one you have.

Why are doses counted in units instead of mL?

A U-100 insulin syringe is calibrated in units, and 100 units is 1 mL. Drawing 0.1 mL on a small barrel is hard to read accurately; drawing 10 units is unambiguous because the unit ticks are clearly visible. Switching the language from mL to units removes the most common source of accidental 10x errors, which is misreading a decimal place. The only mL figure that should appear anywhere in your own notes is the bac water volume you added.

What happens if I add a different volume than planned?

The arithmetic still works, you just have a different concentration, and every unit count you had worked out is now wrong until you recalculate it. Recalculate with the volume you actually used, not the one you intended, and write that number on the vial. The reconstitution calculator on our method page recomputes the unit count for any volume you enter.

Can I shake the vial to make it dissolve faster?

No. Shaking foams the solution and can denature the peptide. Roll the vial gently between your palms or swirl it on a flat surface instead. Full dissolution should take 30 to 60 seconds. If it is taking much longer than that, keep swirling rather than reaching for a faster method.

Does the bac water volume change how much retatrutide is in the vial?

No, and this is the single most useful thing to understand about reconstitution. A 20mg vial contains 20mg of peptide whether you add 1 mL, 2 mL or 3 mL. The water changes the concentration, which changes how many units on the syringe correspond to a given amount in mg. It does not create or remove peptide. That is why two people with identical vials can have completely different unit counts and both be right.

Is there an approved retatrutide dose to reconstitute for?

No. Retatrutide is investigational, has no regulatory approval and no approved dose, so the only figures that exist come from clinical trials (Jastreboff et al., 2023). The mg amounts used on this page are the maintenance arms that phase 2 trial assigned, and they appear here only so the units column has something real to convert. They are not a recommendation, a starting point, or a target for any individual. Any decision about use belongs with a qualified clinician.

Reconstitution

How to Reconstitute Retatrutide

The short answer

Bring the vial to room temperature, wipe both rubber stoppers with alcohol, draw your planned volume of bacteriostatic water into a U-100 insulin syringe, inject it slowly down the inside glass wall, and swirl until clear. Then refrigerate. The only retatrutide-specific part is the arithmetic: a 20mg vial in 1 mL is 20 mg per mL, in 2 mL is 10 mg per mL, and in 3 mL is about 6.67 mg per mL. The volume changes how many units on the syringe correspond to a given amount in mg. It never changes how much peptide is in the vial.

Retatrutide ships as a freeze-dried powder. Before anything else happens it is mixed with bacteriostatic water, a process called reconstitution. The steps are easy. The arithmetic afterwards is where mistakes happen, which is why this page spends most of its length on it.

Education only

Retatrutide is investigational and has no approved dose. Every mg figure on this page is either plain arithmetic or a maintenance arm the phase 2 trial assigned (Jastreboff et al., 2023), included so the unit counts have something real to convert. Nothing here tells any individual what to take. That decision belongs with a qualified clinician.

What bacteriostatic water is, and why it is the one to use

Bacteriostatic water for injection is sterile water containing 0.9 percent benzyl alcohol as a preservative, and it is the standard diluent for multi-use peptide vials. The preservative is what makes a multi-use vial possible at all: it inhibits bacterial growth in the vial between draws.

Bacteriostatic water

Preserved, so the vial reopens

The benzyl alcohol inhibits bacterial growth in the vial between draws. This is the standard diluent for a peptide vial you will enter more than once.

Sterile water

A different product

Sterile water for injection is not bacteriostatic water and does not carry the benzyl alcohol preservative. The two vials look alike, so read the label rather than assuming which one is in front of you.

The retatrutide walkthrough, step by step

About five minutes start to finish. The procedure is the same one on our general reconstitution page, with the volume and storage notes that apply to the 20mg vial. To run the same arithmetic on a different vial strength or a different volume, use the peptide reconstitution calculator.

Set the vials out and wipe both stoppers
If the vial has been in a fridge or freezer, let it reach room temperature before you mix it. Then wipe the rubber stopper of both the peptide vial and the bacteriostatic water vial with a fresh alcohol swab and let each surface air-dry for a few seconds. This is the single biggest contamination guard in the whole process.
Draw your planned bac water volume into a U-100 insulin syringe
Decide the volume before you start, because it sets the concentration for the life of the vial. Peptara Labs defaults to 2 mL for the 20mg retatrutide vial, which is the figure on our reconstitution page and in the protocol dashboards we build. Pull the plunger to that volume, insert the needle into the bacteriostatic water vial, and draw cleanly.
Inject the water slowly down the inside of the glass wall
Push the needle into the retatrutide vial at an angle so the bacteriostatic water runs down the inner glass wall rather than landing directly on the freeze-dried cake. A slow stream protects fragile peptide bonds and keeps the finished solution clear.
Swirl gently until clear, never shake
Roll the vial between your palms or swirl it on a flat surface until the powder is fully dissolved. Shaking creates foam and can fragment the peptide. The solution should look clear within 30 to 60 seconds. If anything is still visibly undissolved, keep swirling rather than shaking.
Refrigerate, and write the volume on the vial
Once mixed, store the vial at 2 to 8 Celsius. Write the bac water volume you actually used on the label, because every unit count you calculate from here depends on that one number and nothing on the vial records it for you.

The math for a 20mg retatrutide vial

One formula covers every volume and every vial strength. Everything below is that formula applied to the 20mg vial.

The formula

units = (amount in mg / vial strength in mg) × (bac water in mL × 100)

A U-100 insulin syringe holds 100 units per 1 mL, so 1 mL of reconstituted solution is 100 units. Put 20mg of retatrutide into 2 mL and the vial holds 200 units in total, each carrying 0.1 mg.

What one unit holds at each volume

Bac water added	Concentration	1 unit holds	10 units	50 units
1 mL	20 mg/mL	0.2 mg	2 mg	10 mg
2 mL (our default)	10 mg/mL	0.1 mg	1 mg	5 mg
3 mL	about 6.67 mg/mL	about 0.067 mg	about 0.67 mg	about 3.33 mg

The vial holds 20mg at every volume in this table. Only the concentration moves.

The same arithmetic in reverse: units for a given amount

The mg column below is the set of weekly maintenance arms the phase 2 trial assigned: 1, 4, 8 and 12 mg (Jastreboff et al., 2023). They appear here because the units column needs real numbers to convert, not because any of them is a dose for anyone. Retatrutide is investigational and has no approved dose.

Amount (research-reported arm)	At 1 mL	At 2 mL	At 3 mL
1 mg	5 units	10 units	15 units
4 mg	20 units	40 units	60 units
8 mg	40 units	80 units	120 units
12 mg	60 units	120 units	180 units

Two limits the arithmetic does not know about. A single 1 mL U-100 syringe holds 100 units, so any cell above 100 is correct as arithmetic but is not one draw. And a count under about 5 units sits in the hardest part of the barrel to read, so draw slowly and check the tick before you commit.

How much bac water should go in

It depends, and the honest version of that answer is short: the volume sets the concentration and nothing else. Peptara Labs defaults to 2 mL for the 20mg retatrutide vial, which is the figure on our reconstitution page and in the protocol dashboards we build. Three things decide whether a different volume makes sense.

Readability of the draw

More water means each unit carries less peptide, so the same amount becomes a larger unit count that is easier to read on the barrel. Less water means smaller draws.

What the syringe can take

A 1 mL U-100 syringe holds 100 units. Dilute far enough and a single draw stops fitting in one syringe, which is a practical ceiling on volume.

What the vial can hold

Check the vial physically takes the volume before you draw it. A volume that does not fit forces an improvised mix, and every unit count calculated from the intended volume is then wrong while still looking authoritative.

Storage, before and after

Before reconstitution

Stable at room temperature

Lyophilized peptide powder is stable at room temperature for weeks and in a freezer for many months. Keep the vial sealed and out of direct sunlight until the day you mix it.

After reconstitution

Refrigerate immediately

Once mixed, store the vial at 2 to 8 Celsius. A 30-day shelf life is the safe default for most peptides. Your protocol dashboard carries the per-peptide detail for what you ordered.

Write it on the vial

The volume you actually added is the one number every later calculation depends on, and nothing on the vial records it. Write it on the label at the moment you mix, along with the date, and the arithmetic stays checkable weeks later.

Six mistakes worth avoiding

Shaking instead of swirling

Shaking foams the solution and can fragment the peptide. Roll or swirl until clear, and give it the full 30 to 60 seconds.

Firing the water straight onto the powder

Angle the needle so the stream runs down the inside of the glass. Hitting the freeze-dried cake directly is rough on the peptide and clouds the solution.

Reading mL where the syringe says units

This is the error that produces 10x mistakes. A U-100 syringe is marked in units, 100 units to 1 mL. Keep every figure except the bac water volume in units.

Using a U-40 syringe by accident

U-40 is a different scale entirely and will not match any unit count worked out for U-100. A half-cc U-100 syringe holds 50 units and is fine; U-40 is not.

Adding a volume the vial cannot hold

Check the vial physically takes the volume before you draw it. A volume that does not fit forces an improvised mix, and the unit counts still read as authoritative afterwards.

Changing the volume and not redoing the math

The unit count is a function of the volume you actually added. Change the water and every number downstream changes with it. Write the volume on the vial so nothing has to be remembered.

Keep reading

The method page, the calculator, and the research behind the numbers

How to reconstitute peptides

The general method for every compound in the catalog, plus a live calculator.

Peptide reconstitution calculator

The same two formulas as a tool, for any vial strength and any volume.

Retatrutide

The 20mg vial this page does the arithmetic for, with its batch COA.

Retatrutide dosage

What the phase 2 trial arms were, research-reported, not advice.

Units vs mg

Why the syringe reads in units and the vial reads in mg.

Peptide injection basics

What happens after the vial is mixed.

Peptide glossary

Plain definitions for bac water, lyophilized, diluent, and the rest.

Reconstituting retatrutide: FAQ

References

Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity, A Phase 2 Trial. New England Journal of Medicine. 2023;389(6):514-526. doi:10.1056/NEJMoa2301972. PMID 37366315.

General educational information only, research-use framing, not medical advice. Retatrutide is investigational and has no approved dose. Consult a qualified professional before acting.