We talked to dozens of experts for our report on how Medicare is wasting hundreds of millions of dollars a year by failing to look into doctors who disproportionately prescribe name-brand drugs. They struggled to explain why some doctors wouldn't routinely pick cheaper generics.

Name-brand drugs are appropriate in certain circumstances, they said: when there are no equivalent generics, when patients have side effects, or if they are particularly sensitive to slight changes in a drug's composition. But these factors should apply to only a small fraction of cases, they said.