Side effects from prescription drugs impact one in four patients, according to a new study published in the New England Journal of Medicine.

“It’s a problem that is common, in many cases the impact could be prevented or reduced, and it has a large impact on patients,” said Tejal Gandhi, an internist at Brigham & Women’s Hospital in Boston and the chief author of the study.

About 3.34 billion prescriptions were handed out in the United States in 2002, according to IMS Health, a provider of pharmaceutical and health care data.

“A lot of problems were going on a long time that weren’t being fixed, either because the patients didn’t tell the doctor or the physicians didn’t change the medication. That was what surprised us,” Gandhi told Reuters.

It is estimated that about 5 percent of hospital admissions - over 1 million per year - are as a result of drug side effects. But most of the cases are not recorded.

(via Reuters)