Iloperidone, also known as Fanapt, Fanapta, and previously known as Zomaril, is an atypical antipsychotic for the treatment of schizophrenia. Iloperidone shows high affinity and maximal receptor occupancy for dopamine D2 receptors in the caudate nucleus and putamen of the brains of schizophrenic patients. The improvement in cognition is attributed to iloperidone's high affinity for α adrenergic receptors. Iloperidone also binds with high affinity to serotonin 5-HT2a and dopamine 3 receptors. Iloperidone binds with moderate affinity to dopamine D4, serotonin 5-HT6 and 5-HT7, and norepinephrine NEα1 receptors. Furthermore, iloperidone binds with weak affinity to serotonin 5-HT1A, dopamine D1, and histamine H1 receptors. Iloperidone is indicated for the treatment of acute schizophrenia.

P-88-8991 (Hydroxy Iloperidone, 4-[3-[4-(6-fluoro-1,2-benzisoxazol-3-yl)-1-piperidinyl] propoxy]- 3-methoxy-methylbenzenemethanol) is the major active metabolite of Iloperidone an atypical antipsychotic that used for the acute treatment of schizophrenia in adults. Metabolic reduction of Iloperidone carbonyl group leads to P-88-8991 in rats, dogs, and humans. The receptor affinity profile of P-88-8991 is comparable to that of iloperidone: this metabolite binds to the serotonin 5-HT2A receptors, adrenergic alpha1 and alpha2C receptors, and D2A receptors and with lower affinity to other monoamine (dopamine, serotonin, and histamine H1 ) receptors. The comparable receptor binding profile of P-88-8991 indicates that it is likely to contribute to the clinical profile of iloperidone. Preclinical experiments, such as the mouse apomorphine climbing test, the rat self-stimulation, and the pole climb avoidance task, indicate antipsychotic activity of P88-8991 and confirm that this metabolite crosses the blood–brain barrier