It is a synthetic analog of ergocalciferol (vitamin D). Ergocalciferol itself and metabolites can be deactivated by 24-hydroxylation. It is an analog of 1,25-dihydroxyergocalciferol, the active form of vitamin D (ergocalciferol). Vitamin D3 (cholecalciferol) is typically absorbed more readily than vitamin D2 (ergocalciferol). Vegan sources of vitamin D include ergocalciferol and synthetic or plant sources of cholecalciferol. Cholecalciferol (vitamin D) and ergocalciferol (vitamin D) are used as rodenticides. Exposure to ultraviolet light causes a photochemical reaction that converts ergosterol to ergocalciferol. VitaminD (ergocalciferol) and vitaminD (cholecaliferol) share a similar mechanism of action as outlined above. Cholecalciferol and ergocalciferol can be ingested from the diet and from supplements. Unlike cholecalciferol, 25-hydroxylation is not performed by CYP27A1 for ergocalciferol. Like cholecalciferol, Ergocalciferol is inactive by itself. Vitamin D2, or ergocalciferol, is obtained from D2 supplements or fortified food sources. Ergocalciferol is available as a generic medication and over the counter. Ergosterol is a biological precursor of vitamin D, the chemical name of which is ergocalciferol. Cholecalciferol is converted in the liver to calcifediol (25-hydroxycholecalciferol); ergocalciferol is converted to 25-hydroxyergocalciferol.