Methods and compositions are provided for treating neuropsychiatric disorders such as schizophrenia, depression, attention deficit disorder, mild cognitive impairment, dementia, and bipolar disorder. The methods entail administering to a patient diagnosed as having a neuropsychiatric disorder (e.g., schizophrenia, depression, attention deficit disorder, mild cognitive impairment, dementia bipolar disorder, etc.) or as at risk for a neuropsychiatric disorder a benzoic acid, benzoic acid salt, and/or benzoic acid derivative, and/or a sorbic acid, sorbic acid salt, and/or sorbic acid derivative, in combination with a neuropharmacological agent (e.g., an antipsychotic, an antidepressant, medications for attention deficit and hyperactivity disorder, cognitive impairment, or dementia, etc.) where the benzoic acid, benzoic acid salt, or benzoic acid derivative, and/or a sorbic acid, sorbic acid salt, and/or sorbic acid derivative, is in an amount sufficient to increase the efficacy of the neuropharmacological agent.