CONTEXT: Dextromethorphan (DXM) abuse persists among US youth and should be closely monitored because of the risks of severe medical complications, addiction, and psychiatric sequelae. Prior investigations have demonstrated DXM to be an emerging drug of abuse with increasing national prevalence through 2004. OBJECTIVE: To extend existing substance abuse survey results by describing demographic, geographic, product, and outcome trends in medically significant DXM abuse cases (those reported to US poison centers). METHODS: National Poison Data System (NPDS) data are collected and compiled in real time by all 57 US poison centers. Demographic, geographic, product, and outcome data for all intentional DXM abuse cases reported to the NPDS between 2000 and 2010 were analyzed. RESULTS: A total of 44,206 DXM abuse cases met inclusion criteria, 34,755 of which were single-substance exposures. The mean annual prevalence of DXM cases reported to poison control centers was 13.4 cases per million population for all ages and 113.0 cases per million for 15-19 year olds. The prevalence of DXM cases for all ages increased steadily (p = 0.002, Cochran-Armitage trend test) until 2006 to a peak of 17.6 calls/million and has subsequently plateaued at 15.7 cases per million in 2010. This trend is also seen in the most commonly abused brand of DXM products, Coricidin(®). A preponderance of male adolescents was noted throughout the study period. The odds of a severe outcome are increased for a multi-substance exposure (OR: 2.53; 95% CI: 2.14-2.99, logistic regression); odds were not significantly increased for any of the most commonly abused product brands. CONCLUSION: The increasing trend of DXM abuse cases noted in the first half of the decade by previous studies seems to have peaked at 17.6 calls per million population in 2006. It is likely that a combination of legislative, educational, and economic initiatives are responsible for the observed plateau.