Identifying possible new biological activities of psychoactive substances belonging to various chemical classes may lead to a better understanding of their mode of action and side effects. We report here that amines structurally related to amphetamine, a widely used psychoactive substance, such as amphetamine, methamphetamine, phentermine, mephentermine, and chlorphenteramine, potently activate several carbonic anhydrase (CA, EC 4.2.1.1) isoforms involved in important physiological functions. Of the 11 investigated human (h) isoforms, the widespread hCA I and II, the secreted hCA VI, as well as the cytosolic hCA XIII, and membrane-bound hCA IX and XIV were poorly activated by these amines, whereas the extracellular hCA IV, the mitochondrial enzymes hCA VA/VB, the cytosolic hCA VII, and the transmembrane isoform hCA XII were potently activated. Some of these enzymes are abundant in the brain, raising the possibility that some of the cognitive effects of such psychoactive substances might be related to their activation of these enzymes.