Compositions and methods comprising bupropion or related compounds for sustained delivery of dextromethorphan

A method, comprising treating a human being with dextromethorphan by administering once or twice daily for at least eight consecutive days a combination of dextromethorphan and bupropion to the human being, wherein the human being is an extensive metabolizer of dextromethorphan, wherein the combination is administered in a dosage form, which prior to being administered to the human being, has been shown to be effective for providing an AUC0-12 of dextromethorphan of about 700 ng·hr/mL to about 1050 ng·hr/mL to an average human being that is an extensive metabolizer of dextromethorphan after eight consecutive days of administering the dosage form, and wherein, prior to being administered to the human being, it has been shown that after eight consecutive days of administering the dosage form to an average human being that is an extensive metabolizer of dextromethorphan, the AUC0-12 of dextromethorphan is at least about 15 times the AUC0-12 of dextromethorphan that would be achieved by administering the same amount of dextromethorphan without bupropion for eight consecutive days.