Ergocalciferol

Ergocalciferol is a form of vitamin D, also called vitamin D₂. It is marketed under various names including Deltalin (Eli Lilly and Company), discontinued Drisdol (Sanofi-Synthelabo), and Calcidol (Patrin Pharma). Created from viosterol when ultraviolet light activates ergosterol (found in fungi, it is named as a sterol from ergot), with fungi as the primary plant source.

Ergocalciferol may be used as a vitamin D supplement, and a 2011 clinical guideline considered it to be as effective as cholecalciferol (vitamin D₃), which is produced naturally by the skin when exposed to ultraviolet light. Conflicting evidence exists for how similarly D₂ and D₃ behave in the body and whether they are equally active, with some studies suggesting D₃ is more potent, while others report equal efficacy. Cholecalciferol (vitamin D₃) is sensitive to UV radiation and rapidly, but reversibly, forms other sterols which can further irreversibly convert to ergosterol.