Chronic treatment with olanzapine (OLZ), an atypical antipsychotic drug, is associated with the adverse effects of weight gain, hyperglycemia and/or hypertriglyceridemia. Green tea or epigallocatechin gallate (EGCG), one of the most abundant green tea polyphenols, significantly reduces or prevents an increase in glucose levels, lipid markers and/or body weight. We hypothesized that combined treatment with OLZ and green tea extract (GTE) or EGCG may prevent body weight gain and increase of the lipid markers. ICR male mice weighing an average of 30.51 g (n=32) at the beginning of the experiment were used. OLZ, OLZ+GTE and OLZ+EGCG were administered for 27 d in the drinking water, and then the levels of fasting glucose, nitric oxide (NO), and a typical lipid marker triglyceride (TG) were determined in plasma. The body weight and food intake were also compared. The chronic treatment of OLZ increased the average body weight compared with that of controls. In the presence of GTE or EGCG, the OLZ-induced increase in body weight was significantly prevented. Furthermore, in the OLZ group, the plasma levels of glucose, NO and TG were significantly increased, whereas GTE or EGCG prevented these increases. These results implicate that OLZ may induce systematic inflammatory reaction, and suggest that GTE or EGCG can protect against OLZinduced weight gain, hyperglycemia and hypertriglyceridemia.