Calcitriol (INN) (; ), also called 1,25-dihydroxycholecalciferol or 1,25-dihydroxyvitamin D₃, is the hormonally active form of vitamin D with three hydroxyl groups (abbreviated 1,25-(OH)₂D₃ or simply 1,25(OH)₂D). It increases the level of calcium (Ca²⁺) in the blood by (1) increasing the uptake of calcium from the gut into the blood, and (2) possibly increasing the release of calcium into the blood from bone.