TPH2 and cocaine dependence: TPH2 activation may be regarded as a new prospective for neuropsychiatric diseases related to brain 5-HT levels.[27] The variants inTPH2 gene was related to the efficacy of disulfiram treatment for cocaine addiction.[28] Since cocaine's mechanism of action is through blockade of dopamine, norepinephrine and serotonin transporters,[29] we also evaluated the role of a functional variant in the TPH2 gene.