has role is protonated form of 13-cis-retinoate retinoic acid antineoplastic agent keratolytic drug teratogenic agent isotretinoin A retinoic acid that is <i>all</i>-<i>trans</i>-retinoic acid in which the double bond which is α,β- to the carboxy group is isomerised to <i>Z</i> configuration. A synthetic retinoid, it is used for the treatment of severe cases of acne and other skin diseases.