The secret about drugs is that they only work in about half of the people who take them

Making Personalized Medicine Pay - BusinessWeek:

"The dirty little secret about drugs is that they only work in about half of the people who take them. So says an educational nonprofit called the Personalized Medicine Coalition, and many drug executives concede as much. Of the $292 billion spent in the U.S. on prescription drugs in 2008, as much as $145 billion went to medications that didn't help individual patients, said Jerel Davis, project manager at McKinsey, at a recent conference. And billions more are being spent to treat adverse drug reactions and other complications. "When you look at the data, it's shocking," says Dr. Robert S. Epstein, chief medical officer at Medco Health Solutions (MHS), a $51 billion company that manages drug prescriptions for 60 million Americans.

Researchers know how to solve this problem. First, figure out the differences between those patients who respond to a drug and those who don't, then treat only to those who will benefit. But this personalized medicine approach 'has been slower to develop than we thought 10 years ago,' says Richard K. Schatzberg, CEO of Generation Health, a startup that offers targeted medicine services. Lack of enthusiasm in the drug industry is a big reason; companies would lose billions of dollars if only those who actually benefit were to use such blockbuster drugs as antidepressants, arthritis medicines, and cholesterol pills...."