Bupropion as a modulator of drug activity

A method of treating major depressive disorder comprising:

• orally administering a dosage form once a day or twice a day for at least 8 consecutive days, to a human being suffering from major depressive disorder;
• wherein the dosage form contains, as the only therapeutically active agents in the dosage form for the treatment of depression, about 90 mg to about 115 mg of bupropion hydrochloride, or a molar equivalent amount of the free base form or another salt form of bupropion, in combination with about 40 mg to about 70 mg of dextromethorphan hydrobromide, or a molar equivalent amount of the free base form or another salt form of dextromethorphan.