Retatrutide Dosage Calculator: Units, Reconstitution and Escalation

Retatrutide is sold as a lyophilised powder measured in milligrams, injected as a solution measured in millilitres, and drawn up on a syringe marked in units. Three different scales, two conversions, and a compound where a decimal place error changes the dose by a factor of ten. The calculator below does the arithmetic and shows the working, because knowing where the number comes from is what stops you trusting a wrong one.

The maths behind it is one division followed by one multiplication. Concentration is vial strength divided by the volume of bacteriostatic water added. Volume per dose is the target dose divided by that concentration. Syringe units are that volume multiplied by the units per millilitre marked on your barrel, which is 100 on a standard U-100 insulin syringe. Nothing else is involved, and any calculator that produces a different answer is using a different assumption somewhere.

Choosing the Bacteriostatic Water Volume

There is no correct amount of bacteriostatic water. The volume you add is a choice about how the dose sits on the syringe, and it changes nothing about how much compound you receive. A 30mg vial reconstituted with 3mL and a 30mg vial reconstituted with 6mL both contain 30mg. The second one simply requires twice the volume to deliver the same dose.

What the choice does affect is measurement error. Every insulin syringe has a practical floor below which the graduations are too fine to read reliably, and for most people that floor sits somewhere around 4 to 5 units. If a target dose lands at 2 units, a one unit misread is a fifty percent dosing error. If the same dose lands at 20 units, the same misread is five percent.

A useful default is to aim for a concentration where your typical dose lands between 10 and 40 units on a U-100 syringe. That range is easy to read, tolerates a small drawing error, and keeps the injection volume comfortable. The other constraint is the vial itself: most research vials will not hold much more than 5mL of liquid, and overfilling one is how a reconstitution goes wrong before the first dose.

The Escalation Table

Retatrutide is not a compound anyone starts at a working dose. The phase 2 programme escalated gradually and the gastrointestinal side effect profile is dose dependent, which means the schedule matters as much as the endpoint. Set your starting dose, the size of each increase and how long you hold each step, and the table converts the whole run into syringe units at your chosen concentration.

The default shown, one milligram to start with one milligram increases held four weeks each, is the conservative pattern. Faster escalation is possible and produces more nausea. The dosage guide covers where the tolerability ceiling usually appears and what the trial escalation looked like, which is the context this table does not supply on its own.

Where the Arithmetic Actually Goes Wrong

Five errors account for most of it, and none of them are unusual.

Reading a U-40 syringe as a U-100

Insulin syringes come in more than one scale. A U-100 barrel is marked so that 100 units equals one millilitre. A U-40 barrel is marked so that 40 units equals one millilitre. The same physical volume reads as a completely different number on each, and drawing to a unit figure calculated for the wrong barrel produces a 2.5 fold dosing error in one direction or the other. Check what is printed on the barrel rather than assuming, and set the calculator to match.

Assuming the powder occupies no volume

It occupies a little. Adding 3mL of bacteriostatic water to a 30mg vial produces slightly more than 3mL of solution, because the dissolved solid contributes its own displacement. For peptide quantities at this scale the effect is well under one percent and is fair to ignore. It is worth knowing about only so that a small discrepancy between the calculated and observed volume does not read as a problem.

Forgetting that label weight is not peptide weight

Lyophilised peptide powder contains residual water and counterions from synthesis alongside the peptide itself. Net peptide content for research grade material typically sits between 70 and 90 percent of the powder mass, so a vial labelled 30mg may contain closer to 25mg of actual retatrutide. Every calculator, including this one, works from label weight, because that is the only figure available. Real delivered doses therefore run modestly below the arithmetic, which is one plausible reason protocols sometimes feel weaker than published research suggests. The peptide testing guide covers how to find out where a specific vial sits.

Injecting bacteriostatic water into the powder at speed

Aim the stream at the glass wall of the vial and let it run down. Firing it directly into the cake, or shaking afterwards, applies shear that can denature part of the peptide. Swirl gently, wait, and let it dissolve on its own. The reconstitution guide covers the full sequence and the retatrutide specific version covers the vial sizes this compound actually ships in.

Not writing the concentration on the vial

Two vials of different strengths reconstituted at different volumes look identical in a refrigerator four weeks later. Write the concentration in mg per mL and the reconstitution date on the vial in permanent marker before it goes away. This costs ten seconds and prevents the only dosing error on this list that cannot be caught by recalculating.

Storage After Reconstitution

A sealed lyophilised vial is stable for a long time at refrigerator temperature and tolerates room temperature shipping without meaningful loss. Once bacteriostatic water goes in, the clock starts. Reconstituted peptide belongs at 2 to 8 degrees Celsius and has a usable life measured in weeks, not months, with the benzyl alcohol in bacteriostatic water doing the antimicrobial work rather than preserving the peptide itself.

This is the practical argument against reconstituting a large vial all at once for a long protocol. A 60mg vial at 4mg per week is fifteen weeks of solution sitting in a refrigerator, which is longer than the material is reliably good for. Splitting a large vial into two reconstitution events, or buying smaller presentations despite the worse cost per milligram, is the trade. The storage guide covers the temperature and light variables in detail.

Comparing Against the Other GLP Compounds

The same arithmetic works for tirzepatide and semaglutide, with different dose ranges. Tirzepatide runs from 2.5mg to 15mg per week and semaglutide from 0.25mg to 2.4mg, so the concentration that puts a retatrutide dose in a readable part of the syringe will not be the right concentration for either of the others. Set the vial and water figures for the specific compound rather than reusing a habit. Apollo lists all three under coded names, as GLP-2 T and GLP-1 S respectively, which makes a like for like price check straightforward.

If you are still choosing between them, the retatrutide versus tirzepatide comparison covers the receptor differences and the semaglutide versus tirzepatide piece covers the two approved ones. The stack builder is the faster route if you want a protocol laid out rather than a single compound compared, and the general reconstitution calculator handles compounds outside the GLP class.

Key Takeaways

• Concentration is vial mg divided by mL of bacteriostatic water, and everything else follows from that one number
• The water volume changes how the dose reads on the syringe and nothing about how much compound you receive
• Aim for a concentration that puts your typical dose between 10 and 40 units on a U-100 syringe
• Check whether the barrel is U-100 or U-40 before drawing, because the same volume reads 2.5 times differently
• Label weight is not peptide weight, so real doses run modestly below the calculated figure
• Write concentration and date on the vial before it goes in the refrigerator
• Reconstituted solution has a usable life in weeks, which is the argument against mixing a very large vial at once

Frequently Asked Questions

How much bacteriostatic water should I add to a 10mg retatrutide vial?

There is no single correct answer, because the water volume changes only how the dose reads on the syringe. A common choice is 1mL, giving 10 mg/mL, at which a 2mg dose reads as 20 units on a U-100 syringe. Adding 2mL gives 5 mg/mL and the same dose reads as 40 units, which is easier to measure but uses more volume per injection. Pick the volume that puts your typical dose between roughly 10 and 40 units and keep it consistent.

How do I convert retatrutide milligrams to syringe units?

Divide the vial strength in milligrams by the millilitres of bacteriostatic water added to get concentration in mg per mL. Divide your target dose by that concentration to get the volume in millilitres. Multiply that volume by 100 for a U-100 insulin syringe, or by 40 for a U-40 syringe. A 30mg vial in 3mL is 10 mg/mL, so a 2mg dose is 0.2mL, which is 20 units on a U-100 barrel.

What is a typical retatrutide starting dose?

The published phase 2 programme escalated from low starting doses upward over months rather than beginning at a working dose, and the gastrointestinal side effect profile is clearly dose dependent. Community protocols commonly start around 1mg to 2mg weekly and increase in similar increments held for several weeks at a time. This is research use information rather than a prescribing instruction, and the escalation table above exists so the arithmetic of whatever schedule you follow is at least correct.

Does the calculator account for net peptide content?

No, and neither does any other calculator, because net peptide content is not printed on the vial. Lyophilised powder contains residual water and counterions alongside peptide, typically leaving 70 to 90 percent of the powder mass as actual compound. Every calculation here works from label weight, so real delivered doses run modestly below the number shown. The only way to know where a specific vial sits is a quantitative assay or an amino acid analysis.

Can I use sterile water instead of bacteriostatic water?

For a single dose used immediately, sterile water works. For a vial that will be drawn from repeatedly over weeks it does not, because sterile water contains no preservative and each needle entry is an opportunity for contamination. Bacteriostatic water contains around 0.9 percent benzyl alcohol, which is what makes multiple withdrawals from one vial reasonable. The benzyl alcohol preserves against microbial growth and does nothing to protect the peptide from degradation.

How long does reconstituted retatrutide last?

Refrigerated at 2 to 8 degrees Celsius, a reconstituted vial has a usable life measured in weeks rather than months. Exact figures are not published for research material and any precise number would be invented. The practical consequence is that reconstituting a 60mg vial for a fifteen week run leaves solution sitting for longer than it is reliably good for, which is the argument for splitting a large vial into two reconstitution events.