Inositol, or myo-inositol, is a water-soluble compound that the body synthesizes from glucose. It is classified as a vitamin-like compound, which does not in all respects meet the definition of a vitamin, but is necessary to e.g. fish at a certain growth stage.
The highest contents of inositol are found in nuts, beans and cereals. However, it is poorly utilisable from these sources. Breast milk also contains a high level of inositol, and cow's milk a lower level. In the human body, inositol is present in high levels in the nervous tissue and in the kidneys. Inositol plays an important role as part of the plasma membrane, and it is also needed in the synthesis of eicosanoids, polyunsaturated fatty acids, as well as in inter-cellular communication.

The inositol content of energy drinks is ca. 20 mg/100 ml. No recommended intake value has been defined for inositol, as it is not an essential nutrient.