Glutamate antagonists such as topiramate have been proposed based on the glutamate hypothesis of schizophrenia because its properties encourage its exploration and possible development as a medication for the treatment of schizophrenia. A randomised, double-blind, placebo-controlled clinical trial was performed on 18- to 45-year-old patients with schizophrenia. Baseline information including vital signs, height, weight, smoking status, demographic characteristics, (past) psychiatric history, medication history and medication-related adverse effects were collected. Patients were randomly assigned to a topiramate or placebo group. Efficacy of medication was measured by administering Positive and Negative Syndrome Scale (PANSS), and tolerability of treatment was recorded on day 0 (baseline), day 28 and day 56. PANSS values (95% confidence interval) at baseline, day 28 and day 56 in the topiramate group were 96.87 (85.37-108.37), 85.68 (74.67-96.70) and 76.87 (66.06-87.69), respectively; compared with 101.87 (90.37-113.37), 100.31 (89.29-111.32) and 100.56 (89.74-111.37) in the placebo group. General linear model for repeated measures analysis showed that topiramate has lowered PANSS values significantly compared with the placebo group. Similar significant decline patterns were found in all three subscales (negative, positive and psychopathology sign). Clinical response (more than 20% reduction in PANSS) was significantly higher in topiramate-treated subjects than controls (50% vs 12.5%). Topiramate can be an effective medication in controlling schizophrenic symptoms, considering its effect on negative symptoms and controlling antipsychotic-associated weight gain.