<prompt> Psoralen-A is used in the treatment of -PemphigusVitiligoPityriasis albaIcthyosis  <response>: Psoralen and many of its derivatives are naturally occurring tricyclic furocoumarins. The derivative most widely used in photochemotherapy is 8 - methoxypsoralen 8MOP, methoxsalen, xanthotoxin which is principally of plant origin but it is available as a synthetic drug. 4, 5, 8-trimethyl psoralen TMP, trioxsalen is a synthetic compound which is less phototoxic after oral administration and is primarily used for the treatment of vitiligo. ijdvl journal of dermatology, psoralens. 