New research shows more than half a million children every year have bad reactions or side effects from medicines that require medical treatment.
Children younger than age 5 are most commonly affected. Penicillin and other prescription antibiotics are among drugs causing the most problems.
The study appears in October's Pediatrics and is base on national statistics on patients' visits to clinics and emergency rooms between 1995 and 2005.
The study's lead author is a pediatrician with Children's Hospital in Boston. Dr. Florence Bourgeois says parents should pay close attention when their children begin taking a medications for the first time, and doctors should tell parents about possible signs of an allergic reaction.
Bourgeois says the data she studied show no deaths, but 5 percent of children were sick enough to require hospitalization.