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Guide
Peptide doses are usually written in micrograms (mcg) or milligrams (mg), and occasionally in international units (IU). This guide explains how they relate: mcg and mg are both units of mass (1 mg = 1000 mcg), while IU measures biological activity and cannot be converted to a mass with a single universal factor. Reference only, not medical advice.
mcg and mg are units of mass
Micrograms and milligrams both measure weight: 1 milligram equals 1000 micrograms. To go from mg to mcg, multiply by 1000; from mcg to mg, divide by 1000. So a 5 mg vial holds 5000 mcg, and a 250 mcg dose is 0.25 mg. This conversion never depends on concentration.
IU measures activity, not mass
An international unit (IU) is defined per substance by its biological activity, set by reference standards rather than weight. Because the mass that corresponds to one IU differs from one substance to another, there is no single mcg-per-IU or mg-per-IU factor that works across peptides. Only use an IU-to-mass conversion published for that specific product.
Where syringe units fit in
The units marked on a U-100 insulin syringe are a third thing entirely: they are volume marks, where 100 units equal 1 mL. They are not mcg, mg, or IU — they tell you how much liquid to draw. To turn a dose in mg into syringe units you also need the solution’s concentration.
Frequently asked questions
How many mcg are in a mg?
There are 1000 micrograms in 1 milligram. Multiply mg by 1000 to get mcg, or divide mcg by 1000 to get mg. For example, 0.5 mg is 500 mcg and 250 mcg is 0.25 mg.
Can I convert IU to mg for a peptide?
Not with a universal factor. IU is defined by biological activity per substance, so the mass of one IU differs between substances. Use only an IU-to-mass figure published for your specific product; otherwise there is no reliable conversion.
Are insulin-syringe units the same as IU?
No. Insulin-syringe units are volume marks on a U-100 syringe (100 units = 1 mL) and measure liquid, not biological activity. IU measures activity. They are unrelated despite both using the word units.
Which unit will my peptide be labeled in?
Most research peptides and GLP-1 medications are labeled in mg or mcg (mass). IU appears mainly for a few hormone products defined by activity. Check your product’s label for which unit it uses.
Is this medical advice?
No. It explains how the units relate and is reference only. It does not recommend a dose. Verify any conversion with the product label and a clinician or pharmacist.