Inositol, (of which the most prominent naturally-occurring form is myo-inositol, cis-1,2,3,5-trans-4,6-cyclohexanehexol), is a carbocyclic polyol that plays an important role as the structural basis for a number of secondary messengers in eukaryotic cells, including inositol phosphates, phosphatidylinositol (PI) and phosphatidylinositol phosphate (PIP) lipids. It is found in many foods, particularly in cereals with high bran content, nuts, beans, and fruit, especially cantaloupe melons and oranges. It is also noticeably present in popular "boost" drinks such as Red Bull. (though in that particular drink, the amount is far too insubstantial to gain the benefits associated with Inositol; it would require about 360 Red Bulls per day to gain these benefits)citation needed]. It can be synthesised by the human body.
Other naturally occurring isomers (though in minimal quantities) are scyllo-, chiro-, muco-, and neo-inositol. Other possible isomers are allo-, epi- and cis-inositol.
myo-Inositol is classified as a member of the vitamin B complex (often referred to as vitamin B8), though it is not considered a vitamin itself because it is not a vital amine (contains no nitrogen) and is synthesised by the human body.