The number of patients treated in a hospital after a bad reaction to medication grew 52% between 2004 and 2008. More than half of the errors involved seniors over the age of 65, according to data from the Agency for Healthcare Research and Quality.

The adverse events were caused either by taking or being given the wrong medication or dosage, which can be from reasons ranging from an overdose to a pharmacy error. Out of 838,000 people, the top five categories of medicines causing injury or illness were corticosteroids (283,700 cases), painkillers (269,400), blood-thinners (218,800), drugs to treat cancer and immune system disorders (234,300), and heart and blood pressure medicines (191,300).

Fifty-three percent of hospitalized patients there for medication-related injuries were over age 65, while 3% were under 18. Children and teenagers comprised 22% of emergency cases. The AHRQ, a division of the U.S. Department of Health and Human Services, also provided data on which patients were treated in an emergency department. Out of the 838,000 people, the majority involve unspecified medicines (261,600), painkillers (118,100), antibiotics (95,100), tranquilizers and antidepressants (79,300), and corticosteroids and other hormones (71,400).

To read more in “Medication-related Adverse Outcomes in U.S. Hospitals and Emergency Departments, 2008,” click here. To see the agency’s 2008 Nationwide Inpatient Sample and 2008 Nationwide Emergency Department Sample, click here.