If you use a beta-blocker called Corgard to prevent migraine headaches, you are taking advantage of an important if obscure element of modern medicine: physicians' ability to prescribe approved medicines for purposes not explicitly sanctioned by the Food and Drug Administration (FDA). Corgard is approved for angina and high blood pressure only, yet migraine sufferers and their physicians know that it has other useful properties as well. These so-called "off-label" uses of drugs are perfectly legal, yet regulators make it all but impossible for manufacturers to inform doctors about such uses. No law or regulation explicitly forbids it, but the FDA treats it as misbranding or fraud. The government has prosecuted numerous drug makers for off-label promotion, with penalties and settlements in the billions of dollars, write Henry I. Miller and Gregory Conko for Reason.