Abstract: Dextromethorphan is a commonly encountered antitussive medication which has found additional therapeutic use in the treatment of pseudobulbar disorder and as an adjunct to opiate use in pain management. Dextromethorphan at high doses has phencyclidine-like effects on the NMDA receptor system; recreational use of high doses has been found to cause mania and hallucinations. The toxicology and pharmacology of the drug in abuse are reviewed, and the historical literature of adverse psychiatric outcomes is assessed. Five new cases of dextromethorphan intoxication that resulted in assault, suicide, and homicide are reported, together with the corresponding toxicology results. Blood concentrations ranged from 300 to 19,000 μg/L. These results are compared with typical concentrations reported in therapeutic use and impaired driving cases. Based on these findings, dextromethorphan should be considered as a potential causative agent in subjects presenting with mania, psychosis, or hallucinations, and abusers are at risk for violent and self-destructive acts.