Dextromethorphan is an opium alkaloid derivative. Dextromethorphan is a drug of abuse. The main risks associated with dextromethorphan are ataxia, central nervous system (CNS) stimulation, dizziness, lethargy and psychotic behavior. Less frequently with large doses seizures and respiratory depression can occur. Nausea, vomiting, constipation and tachycardia may also occur. (toxnet.nlm.nih.gov)