The primary aim of the study is to investigate the efficacy of metformin and topiramate on second-generation antipsychotic-induced obesity. The secondary domain we look at is the adverse effects of both drugs. The investigators hypothesize that metformin and topiramate are effective in treating obesity induced by second-generation antipsychotics.

Inclusion Criteria:

1. Diagnosis: schizophrenia or schizoaffective disorder
2. Age: 20 to 65
3. BMI>27
4. Receiving second-generation antipsychotics(Olanzapine, Clozapine, Quetiapine, Risperidone, Amisulpride, Zotepine)

Exclusion Criteria:

1. Allergy to metformin or topiramate
2. Currently taking metformin or topiramate
3. Currently taking drugs that may interact with topiramate, including carbamazepine, eslicarbazepine, oxcarbazepine, phenobarbital, phenytoin, primidone, amitriptyline, lithium, metformin, propranolol, and sumatriptan.
4. Being pregnant or planning to become pregnant during the study period,
5. History of hypertension, DM, liver or renal function impairment, cardiovascular disease, CVA, or neurological disorders
6. History of hypoglycemia
7. History of suicidal attempt
8. Current scale of Hamilton Depression Rating Scale>8