The Food and Drug Administration (FDA) approves drugs for sale in the United States when it determines that the clinical benefits of a drug outweigh its potential health risks. To make this decision, FDA reviews supporting data collected from several thousand patients during the drug's development. Once a drug is approved for marketing and used by potentially thousands of patients, however, the type, rate, and severity of adverse events caused by the drug can be much different than those seen during the drug's development. In some cases, FDA or drug manufacturers have removed from the market drugs that have been shown to have unacceptable health risks once they were in widespread use. GAO found that 10 prescription drugs have been withdrawn from the U.S. market since January 1, 1997. Eight of the 10 prescription drugs posed greater health risks for women than for men: four of these may have led to more adverse events in women because they were prescribed more often to women than to men, while the other four had more adverse events in women even though they were widely prescribed to both men and women. Of the two remaining withdrawn drugs, one belongs to a class of drugs known to pose a greater health risk for women, but GAO was unable to find direct evidence that the adverse events that contributed to its withdrawal occurred predominantly in women. GAO found no evidence that the health risks for the remaining withdrawn drug differed for women and men.