Calcipotriol is a synthetic derivative of calcitriol or vitamin D. It is used in the treatment of psoriasis. This medication is safe for long term application in psoriatic skin condition. The efficacy of calcipotriol in the treatment of psoriasis was first noticed by the observation of patients receiving various forms of vitamin D in an osteoporosis study. Unexpectedly, some patients who also suffered from psoriasis experienced dramatic reductions in lesion counts. The precise mechanism of calcipotriol in remitting psoriasis is not well-understood. However, it has been shown to have comparable affinity with calcitriol for the vitamin D receptor (VDR), while being less than 1% as active as the calcitriol in regulating calcium metabolism. The vitamin D receptor belongs to the steroid/thyroid receptor superfamily, and is found on the cells of many different tissues including the thyroid, bone, kidney, and T cells of the immune system.