An analysis of records from the National Poison Data System from a 10-year period ending in 2011 identified 294 reported incidents of people developing adverse symptoms after ingesting 35% (high-concentration) hydrogen peroxide (H202). Among these, 41 (13.9%) experienced an embolic event such as seizure, stroke, or pulmonary embolism, and 20 (6.8%) died or became disabled as a result. Other symptoms included altered mental status, respiratory distress, and hypoxia (lack of blood in the tissues). Consumption of H202 can be dangerous even in small amounts -- one of the deaths reported occurred from drinking just 15 ml (0.5 oz) of hydrogen peroxide liquid ().
For more information, see our CL Answer about drinking hydrogen peroxide.