unit:IU-PER-MilliGM

International Unit per milligramme. The magnitude of one $IU/mg$ depends on the material, so there is no single conversion multiplier. Following the mass-equivalent treatment of $IU$ (see unit:IU), $IU/mg$ is a mass-equivalent per mass and is therefore dimensionless. It is a potency, not a mass fraction (see quantitykind:AmountOfBiologicallyActiveSubstancePerMass).