WEDNESDAY, March 6 (HealthDay News) -- Analyzing the search history of Internet users can turn up unreported side effects of drugs or drug combinations, according to a new study.

By analyzing a year of search history from 6 million Internet users who consented to share anonymous logs of their online searches, the researchers identified an interaction between two drugs that was unknown when the data was gathered in 2010.

The interaction between the antidepressant drug paroxetine (marketed as Paxil) and the cholesterol-lowering drug pravastatin (marketed as Pravachol or Selektine) increases a patient's risk of developing high levels of blood sugar (hyperglycemia).

The researchers had previously identified this interaction by using an automated method of analyzing U.S. Food and Drug Administration data. They then decided to find out if they could pinpoint this interaction by mining Internet users' search data.

The new study appears in the March 6 issue of the Journal of the American Medical Informatics Association.

"Seeking health information is a major use of the Internet now," study co-author Dr. Russ Altman, a professor of bioengineering, genetics and medicine at Stanford University School of Medicine in Stanford, Calif., said in a university news release. "So we thought people are likely typing in drugs they are taking and the side effects they are experiencing and that there must be a way for us to use this data."

The FDA encourages doctors to report any possible drug side effects, but such reporting is voluntary and relies on a doctor or patient noticing something unusual.

"Historically, it's been really hard to detect synergistic effects of drug combinations that aren't necessarily side effects of any of the drugs alone," Altman said.

"I believe patients are telling us lots of things about drugs, and we need to figure out ways to listen," said Altman. Analyzing Internet users' search data is one way to do that.

This method also has been used to track flu outbreaks. A 2010 study found that examining the location and frequency of online searches about the flu and flu symptoms was as accurate at following the flu's spread as the hospital-based tracking methods used by the U.S. Centers for Disease Control and Prevention.

More information

The U.S. Food and Drug Administration explains how consumers can report problems with drugs and other medical products.