Bupropion as a modulator of drug activity

A method of treating major depression, comprising:

• orally administering a dosage form once a day or twice a day for at least 7 days, to a human being suffering from major depression, wherein bupropion and dextromethorphan are the only therapeutically active compounds in the dosage form, wherein the human being receives a daily dose of the bupropion that is about 200 mg to about 250 mg, wherein the daily dose of the bupropion is orally administered once a day or is a total of two twice daily doses of the bupropion, wherein the human being receives a daily dose of the dextromethorphan that is about 60 mg to about 100 mg, wherein the daily dose of the dextromethorphan is orally administered once a day or is a total of two twice daily doses of the dextromethorphan, wherein orally administering the bupropion in combination with the dextromethorphan results in the human being experiencing a therapeutic effect;
• wherein the dosage form provides immediate release of dextromethorphan and sustained release of bupropion;
• and wherein orally administering the dosage form is more effective in treating major depression than orally administering the same amount of the dextromethorphan alone for the same number of consecutive days.