Adverse Drug Events in U.S. Hospitals

HCUP Statistical Brief #234

An adverse drug event (ADE) involves harms to patients caused by medication use. Adverse Drug Events in U.S. Hospitals, a statistical brief from the Healthcare Cost and Utilization Project, presents characteristics of hospital inpatient stays involving an ADE from 28 States in 2010 and 2014. ADE-related stays are reported by the origin of the ADE: those that originated during the inpatient stay versus those that were present on admission to the hospital. The most common causes of ADEs are presented overall and based on origin of the ADE.

ADEs are the leading type of nonsurgical adverse event occurring in hospitals in the United States, with an estimated 1.9 million events in 2010. Some ADEs are the result of medication errors that may occur when a drug is prescribed or administered improperly, but ADEs also may occur when medications are taken correctly. Overall, patients hospitalized with an ADE have an increased length of stay, higher costs, and increased risk of in-hospital death compared with those not experiencing an ADE.

ADEs are increasingly common, in part because of the substantial increase in prescription drug use. Between 2011 and 2014, 91 percent of U.S. adults aged 65 years and older reported use of a prescription drug in the past 30 days, compared with 74 percent reporting prescription drug use between 1988 and 1994. The percentage of Americans aged 65 years and older who reported taking five or more drugs increased from 14 to 41 percent over the same time period. Preventing ADEs is a top priority in health care in the U.S.


  • The overall number of hospital stays involving an ADE remained relatively stable from 2010 to 2014, but stays shifted from ADEs that originated during the stay to ADEs that were present on admission. In 2014, 70.5 percent of ADEs were present on admission, compared with 61.0 percent in 2010.
  • Antibiotics and anti-infectives, systemic agents, and hormones were the most common specific causes of ADE-related hospital stays.
  • From 2010 to 2014, the rate of stays involving an ADE increased the most for ADEs caused by smooth muscle and respiratory drugs (up 24 percent) and decreased the most for ADEs caused by cardiovascular drugs (down 18 percent).
  • Among ADEs that originated during the hospital stay:
    • Rate of stays decreased 24 percent, but the average cost, length of stay, and mortality rate increased (27, 19, and 12 percent, respectively).
    • Rate of stays decreased most for cardiovascular drugs; average costs and length of stay increased most for water, mineral, and uric acid metabolism drugs.
  • Among ADEs that were present on admission:
    • Rate of stays increased 16 percent, and average costs increased 15 percent; length of stay and mortality rate remained relatively stable.
    • Rate of stays increased most for systemic agents; average costs increased most for sedatives or hypnotics.

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Page last reviewed January 2018
Page originally created January 2018
Internet Citation: Adverse Drug Events in U.S. Hospitals. Content last reviewed January 2018. Agency for Healthcare Research and Quality, Rockville, MD.