Dihydrotachysterol (DHT) is a synthetic vitamin D analog activated in the liver that does not require renal hydroxylation like vitamin D<sub>2</sub> (ergocalciferol) and vitamin D<sub>3</sub> (cholecalciferol). DHT has a rapid onset of action (2 hours), a shorter half-life, and a greater effect on mineralization of bone salts than does vitamin D.