Reconstituting a freeze-dried peptide is an arithmetic problem before it is anything else. Get the concentration wrong and every dose that follows is wrong by the same factor. This guide explains the three numbers involved, how to read them off a U-100 insulin syringe, and where people most often slip up. There is a calculator further down that does the sum for you.
Read this first. Peptides sold as "research chemicals" — including BPC-157 and TB-500 — hold no marketing authorisation from the MHRA. They are not licensed medicines in the United Kingdom and they are not approved for human use. Sovital does not sell them and this article does not recommend their use. It is published as a reference on the arithmetic of dilution, which is the same arithmetic whatever is in the vial.
What "reconstitution" actually means
Peptides are supplied as a lyophilised powder — freeze-dried to a dry cake sitting in the bottom of a sealed glass vial. In that state the peptide is stable. It is also unusable, because there is no way to measure out a fraction of a dry cake with any precision.
Reconstitution is the step of adding a sterile liquid, normally bacteriostatic water, to dissolve the powder into a solution of known strength. Once it is in solution you can draw off a measured volume, and that volume corresponds to a known quantity of peptide.
The important consequence is this: the vial does not tell you your dose. A 10 mg vial is 10 mg whether you dissolve it in 1 mL or 3 mL. What changes is the concentration, and therefore how much liquid you draw to get any given amount. Two people with identical vials who added different amounts of water will draw to completely different marks for the same dose.
The three numbers
Every reconstitution calculation uses exactly three inputs:
- How much peptide is in the vial, in milligrams. This is printed on the label.
- How much liquid you add, in millilitres. This is your choice, and it is the number that sets the concentration.
- How much you intend to draw, in milligrams or micrograms.
From those, two steps give you the answer.
Step one — concentration. Divide the peptide by the liquid:
concentration (mg/mL) = peptide in vial (mg) ÷ water added (mL)
Step two — volume to draw. Divide your intended amount by that concentration:
volume (mL) = amount to draw (mg) ÷ concentration (mg/mL)
That is the whole of it. Everything else is unit conversion.
A worked example
Take a 10 mg vial and add 2 mL of bacteriostatic water.
Concentration is 10 ÷ 2 = 5 mg per mL.
Suppose you want 0.5 mg. Volume is 0.5 ÷ 5 = 0.1 mL.
Now add 3 mL to the same vial instead. Concentration becomes 10 ÷ 3 = 3.33 mg/mL, and the same 0.5 mg dose now needs 0.15 mL — half again as much liquid for exactly the same quantity of peptide. Neither is more correct than the other. They are simply different dilutions, and this is precisely why a volume quoted by someone else is meaningless unless you also know what they put in the vial.
Units and millilitres are not the same thing
This is the single most common and most consequential error, so it is worth being slow about.
Insulin syringes are not marked in millilitres. They are marked in insulin units, and the scale runs from 0 to 100 along the barrel. On a U-100 syringe — the standard type, and the one almost everyone uses for this — the relationship is fixed by definition:
100 units = 1 mL
So one unit is a hundredth of a millilitre, and converting is a matter of multiplying by 100:
- 0.1 mL is 10 units
- 0.25 mL is 25 units
- 0.42 mL is 42 units
- 1 mL is 100 units — the entire syringe
The danger is that "0.1" and "10" are both small, plausible-looking numbers. Someone reading 0.1 mL and drawing to the 1 mark on the barrel has taken a tenth of what they meant to. Someone reading 10 units and interpreting it as 10 mL has asked for ten times a full syringe. Always know which unit you are working in before the needle goes near the vial.
Note also that most 1 mL insulin syringes mark every 2 units, not every unit. An odd-numbered result falls between two marks, and anything under 2 units cannot be measured on the barrel at all. If your calculation lands there, the practical fix is to use less water next time, which raises the concentration and gives a larger, more readable draw for the same amount of peptide.
Work it out
Enter your three numbers below. The syringe shows where the plunger would sit.
Where it goes wrong
Assuming someone else's volume applies to you
"Draw 20 units" is not information unless the vial size and the water volume come with it. The same instruction produces wildly different quantities depending on the dilution. Always recalculate from your own vial.
Micrograms read as milligrams
There are 1,000 micrograms in a milligram. Protocols circulating online are often quoted in micrograms while vials are labelled in milligrams. Mixing the two up gives an error of a thousandfold, in whichever direction you got it wrong.
Injecting the water too hard
Bacteriostatic water is directed down the inside wall of the vial so it runs onto the powder gently. Peptides are fragile molecules and a jet fired straight into the cake can damage them. The vial is then left to dissolve on its own, or swirled slowly — never shaken.
Treating the result as exact
Vial fill tolerances, residual volume left in the needle and hub, and the difficulty of reading between marks all mean the real figure drifts from the calculated one. The arithmetic is exact; the physical world is not.
Storage after mixing
A dry vial is stable for a long time. Once reconstituted, the clock starts. Solutions are refrigerated, kept out of light, and have a far shorter usable life than the powder did. Bacteriostatic water contains a preservative, typically benzyl alcohol, which is what distinguishes it from sterile water; sterile water has no preservative and offers no protection against microbial growth after the first needle entry.
A word on GLP-1 medicines
Semaglutide and tirzepatide are in a different legal category from everything else discussed here, and the distinction matters.
They are licensed prescription-only medicines in the United Kingdom, sold under brand names including Ozempic, Wegovy and Mounjaro. They are lawfully available only on prescription, following assessment by a prescriber who takes responsibility for the decision.
Licensed GLP-1 products are supplied as pre-filled injection pens with a built-in dose selector. They do not arrive as powder and they are never reconstituted. There is no calculation for the patient to perform — the dose is set by turning a dial.
The practical consequence is blunt. If you are holding a vial of GLP-1 powder that needs mixing, you are not holding a licensed UK medicine. It has come from outside the regulated supply chain, nobody has verified its contents, and no prescriber is overseeing its use. The calculator on this page will not make that situation safe, and it is not offered for that purpose.
This is not a theoretical concern. The MHRA has issued repeated warnings about unlicensed weight-loss injections sold online, and people in the UK have been hospitalised after self-administering them — in several reported cases through exactly the units-versus-millilitres confusion described earlier in this article, taking ten times the amount intended. Because these drugs act powerfully on blood glucose, that class of error can be life-threatening rather than merely wasteful.
If you want to use a GLP-1 medicine, the route is a prescriber — your GP, or a registered pharmacy service. That way the product is genuine, the dose is appropriate to you, and someone qualified is watching for side effects.
Legal position in the United Kingdom
This section is a plain summary, not legal advice, and it is current as at publication.
BPC-157, TB-500 and similar peptides have no UK marketing authorisation. They have not been assessed by the MHRA for safety, quality or efficacy, and no manufacturer has brought them through the licensing process for human use. They are commonly sold labelled "for research use only", which is a distinction with real legal weight: it is the basis on which they can be supplied at all.
Selling or supplying them for human consumption, or advertising them as if they were medicines, falls foul of the Human Medicines Regulations 2012. Separately, several of these compounds appear on the World Anti-Doping Agency Prohibited List under S0, the class covering substances with no current approval from any governmental regulatory health authority. Tested athletes should treat that as decisive.
Because these substances are unlicensed, there is no regulated supply chain behind them. Independent testing of products sold in this market has repeatedly found discrepancies between labelled and actual content, including underfilled vials, incorrect compounds and contamination. Nothing in the calculation above protects against a vial that does not contain what the label claims.
Medical disclaimer. This article explains dilution arithmetic for reference. It is not medical advice and it is not an endorsement or recommendation to use any substance mentioned. It does not describe doses, protocols or therapeutic uses. Decisions about any injectable substance should be taken with a qualified healthcare professional who knows your history. If you are unwell, or you think you have reacted badly to something you have taken, contact a doctor or call NHS 111.
In short
- Concentration is the vial strength divided by the water you added — you set it, and you can change it.
- Volume to draw is your intended amount divided by that concentration.
- On a U-100 syringe, 100 units is 1 mL, so multiply millilitres by 100 to get units.
- A volume from someone else is meaningless without their vial size and water volume.
- These peptides are not licensed medicines in the UK and are not approved for human use.
- GLP-1 medicines are prescription-only and come as pre-filled pens — a powder vial needing reconstitution is not a licensed product.
