What Are Some Differences Between Milligrams and International Units?


Quick Answer

The chief difference between a milligram and an International Unit is that a milligram is a measure of mass, whereas an International Unit measures the potency of a substance being used in a medical context. In addition, milligrams are part of the metric system and International Units are not.

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Full Answer

International Units quantify the potency of biologically active substances, such as medication, vitamins, and vaccines. There is no single, set International Unit -- it is merely an agreed-upon standard for each individual substance. For example, an International Unit of vitamin A has a very different mass from an International Unit of vitamin C, because the two substances differ in their potency.

Milligrams, on the other hand, measure mass. They are a subunit of the kilogram, the standard metric unit of mass. Milligrams do not differ from substance to substance, as International Units do: a milligram of vitamin A is identical to a milligram of vitamin C.

International Units for a given substance are determined by the World Health Organization's Expert Committee on Biological Standardization. Milligrams are based on the kilogram, and do not have a governing committee.

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