Dihydrotachysterol is hydroxylated in the liver to 25-hydroxydihydrotachysterol, which is the major circulating active form of the drug. It is available in tablet form and the inactive ingredients of dihydrotachysterol are butylated hydroxyanisole, FD&C Red No. 3 (0.2 mg only), lactose, magnesium stearate, propyl gallate, starch, and sucrose. Dihydrotachysterol functions as a blood calcium regulator. Dihydrotachysterol functions effectively by increasing the serum calcium levels and it also renal phosphate excretion. Unlike parathyroid extract, dihydrotachysterol is active when administered orally, and functions by exerting a slow but consistent effect, and can be used for extended periods without increasing the dosage or causing tolerance. Dihydrotachysterol is faster than pharmacologic doses of vitamin D and is less persistent after stopping the treatment, thereby reducing the risk of accumulation and of hypercalcemia.

Dihydrotachysterol is a type of Vitamin D (specifically, \"D4\") used as a medication.