Risperidone hydrochloride is a serotonin 5-HT2 receptor blocker and a potent dopamine D2 receptor antagonist, with Kis of 0.16, 1.4 nM for 5-HT2 and D2 receptor, respectively. 5-HT2 Receptor|0.16 nM (Ki)|D2 receptor|1.4 nM (Ki) Risperidone is serotonin 5-HT2 receptor blocker as shown by displacement of radioligand binding (Ki=0.16 nM), activity on isolated tissues (EC50=0.5 nM). Risperidone is also a potent dopamine D2 receptor antagonist as indicated by displacement of radioligand binding (Ki=1.4 nM), activity in isolated striatal slices (IC50=0.89 nM). Risperidone increases the production of IL-10 and MDC as well as the proinflammatory cytokines, such as IL-6, IL-8, and TNF-α, but decreases the production of IP-10 and IL-12. Long-Evans rats receive daily subcutaneous injections of vehicle or 1 of 2 doses of risperidone (1.0 and 3.0 mg/kg per day) from postnatal Days 14 to 42. Weight gain during development is slightly yet significantly reduced in risperidone-treated rats. In the first 2 experiments, early-life Risperidone administration is associated with increased locomotor activity at 1 week post administration through approximately 9 months of age, independent of changes in weight gain.