Units, IU and milligrams: what the numbers on a vial mean

A plain explanation of the words, not instructions. Delty never calculates or suggests a dose.

This page explains terminology only. It does not tell you what to take, how much water to add, or how to fill a syringe. Your dose comes from your clinician or pharmacist, and any question about it belongs with them.

“Units” is not an amount

This is the single most repeated confusion in peptide communities, and it is worth stating plainly: a number of units describes a distance along a syringe barrel, not a quantity of substance. Two people can hold identical vials, draw to the same mark, and take completely different amounts, because the amount depends on how much liquid was added to the powder.

A unit only becomes an amount once you also know the concentration, which is how much substance is in each millilitre of liquid. Written down without that, a dose in units is not a record anyone can interpret later, including you.

The three things printed on vials

Milligrams (mg) and micrograms (mcg) are masses. A thousand micrograms make a milligram, so these convert to each other and always mean the same quantity.

International units (IU) are different. An IU is defined by biological activity, separately for each substance, so an IU of one thing is not comparable to an IU of another, and IU cannot be converted to milligrams without knowing which substance you are talking about. Some things, including human chorionic gonadotropin and growth hormone, are ordinarily written in IU, which is why an app that only offers mg and mcg is a poor fit for them.

Millilitres (mL) are volume, which is what a syringe actually measures. A common insulin syringe is marked in one hundred parts per millilitre, so one of those marks holds one hundredth of a millilitre.

What reconstitution changes

Many peptides arrive as a freeze-dried powder and are mixed with bacteriostatic water before use. The powder does not change. What changes is the concentration, because the same amount of substance is now spread through however much liquid was added.

Add less liquid and each mark on the syringe carries more substance. Add more and each mark carries less. This is why the volume of water is part of the record rather than a detail you can forget, and why a dose copied from someone else is not meaningful unless their vial was mixed the same way.

What to write down

If you record only one thing, record enough to reconstruct the arithmetic later. That means the vial as labelled, the liquid you added, the date you mixed it, and then for each dose the date, the amount as your clinician expressed it, and where you injected.

The test of a good record is not whether it looks tidy. It is whether you can answer a question months later: what were you taking in June, when did it change, and how did you feel in the days after.

Where Delty fits

Delty is a record, not a calculator. It stores what your clinician told you and what you actually did, in whichever unit you were given, including IU. It keeps your vial dates and the certificate you were sent, and it can produce a one-page summary for an appointment. It does not compute a dose, suggest one, or check one for you.

Your record stays on your iPhone. See our privacy policy for the optional services that are the exceptions.

Nothing here is medical advice, and no peptide discussed in general terms is endorsed or recommended. Talk to a clinician or pharmacist about dosing, side effects and whether something is appropriate for you.

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