ACP-103 reduces haloperidol-induced akathisia, a debilitating extrapyramidal side effect (EPS), in patients with schizophrenia. ACP-103 is a 5-HT2A inverse agonist, to reduce the side effects associated with antipsychotic drug treatment with haloperidol. ACP-103 reduced both the motor disturbances and hyperprolactinemia, a condition of elevated prolactin secretion, caused by haloperidol treatment.