A simple swipe of the card could inform your physician right away if a drug being considered will help you - or even hurt you.

This is the kind of promise behind President Obama's $215 million initiative to develop personalized medicine.

"We've arrived at the point where this could happen, and is going to happen," Francis Collins, director of the National Institutes of Health, said at a recent biotechnology conference in Philadelphia.

A newly published study by researchers at the University of Pennsylvania is another step on the path.

The study, which appears this month in the journal Cell, came from a curious case regarding a class of anti-diabetes drugs known as thiazolidinediones (TZDs). TZDs are highly effective - in some people. But for 20 percent to 30 percent of patients, they are useless and can even cause serious side effects.