Bupropion as a modulator of drug activity

A method of treating nicotine addiction associated with smoking tobacco comprising administering a combination of a therapeutically effective amount of bupropion, or a pharmaceutically acceptable salt thereof, and a therapeutically effective amount of dextromethorphan, or a pharmaceutically acceptable salt thereof, daily for at least 21 consecutive days to a person suffering from nicotine addiction, wherein the person is an ad-lib tobacco smoker, wherein the combination is in a single dosage form and there are no other therapeutically active agents in the dosage form, wherein the dosage form is administered to the person once daily for three days, followed by twice daily, and wherein the method is more effective than administering the same amount of bupropion, or a pharmaceutically acceptable salt thereof, alone.