Latest AHRQ Hospital Data: Over One Million Patients Experience Adverse Drug Event in ’04

In 2004, 1.2 million hospitalized patients experienced an adverse drug event, 90 percent of which were due to a side effect from a medication that was properly administered. Average total hospital costs for patients who experienced drug side effects or other adverse drug events were $10,100, compared with an average cost of $7,600 for patients who didn't experience adverse drug events.
http://www.hcup-us.ahrq.gov/reports/statbriefs/sb29.pdf