Inositol is a vitamin-like substance. It is found in many plants and animals. It is also produced in the human body and can be made in a laboratory. Inositol can be found in many forms (called isomers). The most common forms are myo-inositol and D-chiro-inositol.Inositol is used to for metabolic syndrome and polycystic ovary syndrome (PCOS). It's also used for many other conditions, but there is no good scientific evidence to support most of these uses.