It is of no surprise then, that kynurenic acid levels are elevated in patients experiencing schizophrenia [164], and that 1-methyl-D-tryptophan reverses the physiological indicators of ketamine-induced schizophrenia by acting as an inhibitor to indoleamine 2,3-dioxygenase, the enzyme that generates kynurenic acid from both L- and D-tryptophan [27]. The gene discussed is IDO2; the disease is schizophrenia.