Combinations of 5-HT2A inverse agonists or antagonists such as pimavanserin with antipsychotics such as risperidone are shown to induce a rapid onset of antipsychotic action and increase the number of responders when compared to therapy with the antipsychotic alone. These effects can be achieved at a low dose of the antipsychotic, thereby reducing the incidence of side effects. The combinations are also effective at decreases the incidence of weight gain and increased glucose or prolactin levels caused by the antipsychotic.