Inositol 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. Inositol is found in many foods, in particular, in cereals with high bran content, nuts, beans, and fruit, especially cantaloupe, melons and oranges.

Inositol is not considered a vitamin itself because it can be synthesised by the body. Doses of 12–18 grams per day have been shown to be effective in double-blind trials as an intervention for depression, anxiety, and obsessive-compulsive disorder.