Bupropion as a modulator of drug activity

A method of improving the efficacy of bupropion in treating major depression, comprising:

• orally administering a dosage form once a day or twice a day for at least 14 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 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 twice daily doses of the dextromethorphan, wherein orally administering the bupropion in combination with the dextromethorphan is more effective in treating major depression than orally administering the same dosage regimen of the bupropion without the dextromethorphan;
• and wherein the dosage form provides immediate release of dextromethorphan and sustained release of bupropion.