Clozapine is a partial agonist at cloned, human serotonin 5-HT1A receptors.

Clozapine exhibited 10-fold higher affinity than haloperidol for human 5-HT1A receptors expressed in Chinese Hamster Ovary cells (CHO-h5-HT1A) (Kis = 160 and 1910 nM respectively). Whereas haloperidol did not alter the basal binding of [35S]GTP gama S to CHO-h5HT1A membranes, clozapine stimulated it with an EC50 of 2320 nM and an efficacy of 49% (compared to 5-HT). The stimulation was antagonized by the selective 5-HT1A receptor antagonist, WAY 100635 (1 nM).