The present disclosure is related to methods of treating agitation and/or aggression and/or associated symptoms in subjects with dementia, including, dementia associated with Alzheimer's disease. The method includes administering to a subject in need thereof a dextromethorphan compound, or a pharmaceutically acceptable salt thereof, in combination with quinidine, or a pharmaceutically acceptable salt thereof. The disclosure in certain aspects is also related to compositions that are used for treating agitation and/or aggression and/or associated symptoms in subjects suffering from Alzheimer's disease.
