Ergocalciferol is used in the treatment of hypoparathyroidism (condition in which the body does not produce enough parathyroid hormone), refractory rickets (softening and weakening of bones that does not respond to treatment), and familial hypophosphatemia (rickets or osteomalacia caused by an inherited condition with a decreased ability to break down vitamin D in the body). Ergocalciferol is in a class of medications called vitamin D analogs.