The present invention relates to a method of decreasing cholesterol or low density lipid protein in a subject in need thereof comprising: administering to said subject a pharmaceuticaly effective amount of a composition comprising dextromethorphan.The present invention also relates to a method of treating a subject suffered from bipolar II disorder, comprising administering to said subject a therapeutically effective amount of valproic acid and at least one agent selected from the group consisting of dextromethorphan and memantine, wherein the dose of dextromethorphan or memantine is a low dose not sufficient to work as a N-methyl-D-aspartate (NMDA) receptor antagonist.The present invention further relates to a composition for treating bipolar II disorder, which comprises valproic acid and at least one agent selected from the group of dextromethorphan and memantine, wherein the dose of dextromethorphan or memantine is a low dose not sufficient to work as a N-methyl-D-aspartate (NMDA) receptor antagonist.
