IU
International Unit — a measurement of a biological substance defined by its biological activity rather than its mass, used for hormones like HGH and insulin.
IU is most commonly encountered in the peptide world when discussing growth hormone (HGH), where doses are expressed in IU rather than mcg or mg. The IU value for a given hormone is established by international standards and can vary between substances — 1 IU of HGH is approximately 0.33 mg, but this ratio is substance-specific.
Unlike mcg or mg, IU cannot be directly converted to mass without knowing the specific compound and its potency standard. For peptides like BPC-157 or TB-500, doses are almost always expressed in mcg or mg — IU notation is primarily relevant for HGH and insulin.