HRH1 and schizophrenia: The back metabolite clozapine is a commonly used sedative and antipsychotic drug in schizophrenia with many endogenous targets, including low-high affinity antagonistic actions at D1, D2, and D4 dopaminergic receptors, 5-HT2A, 5-HT2C, 5-HT3, 5-HT6, and 5-HT7 serotonergic receptors, H1 histamine receptors, and α1 and α2 adrenergic receptors, among others (Fitton and Heel, 1990; Ashby and Wang, 1996).