Bupropion as a modulator of drug activity

A method of treating major depressive disorder, comprising administering a dosage form by mouth once daily or twice daily to a human patient in need thereof for at least 8 consecutive days, wherein the dosage form comprises about 105 mg of bupropion hydrochloride and about 45 mg of a dextromethorphan salt as the only therapeutically active compounds in the dosage form;

• and the dosage form is formulated to provide sustained release of bupropion and immediate release of dextromethorphan, wherein the human patient does not experience an adverse event as a result of receiving the dosage form, and wherein the adverse event is insomnia.