Compounds and combinations thereof for treating neurological and psychiatric conditions

A method of treating agitation associated with Alzheimer's disease, comprising administering a first dosage form once daily for one week, to a human patient in need thereof, and then administering the first dosage form twice daily to the human patient for one week, wherein the human patient does not have hepatic impairment, wherein the first dosage form comprises 30 mg of dextromethorphan hydrobromide and 105 mg of bupropion hydrochloride, and wherein after the first dosage form is administered once daily for one week followed by twice daily for one week to the human patient, the method further comprises administering a second dosage form twice daily to the human patient for at least one week, wherein the second dosage form comprises 45 mg of dextromethorphan hydrobromide, or a molar equivalent amount of another salt form of dextromethorphan or the free base form of dextromethorphan, and 105 mg of bupropion hydrochloride, or a molar equivalent amount of another salt form of bupropion or the free base form of bupropion, and wherein after the first dosage form is administered once daily for one week followed by twice daily for one week to the human patient, the method further comprises administering a second dosage form twice daily to the human patient for at least one week, wherein the second dosage form comprises 45 mg of dextromethorphan hydrobromide and 105 mg of bupropion hydrochloride.