Except perhaps for head colds, headaches are probably the most common human ailment. Three out of four Americans had a headache during the past year, according to the National Headache Foundation. Usually, headaches are merely passing annoyances that go away with aspirin or after a nap, but as many as 45 million people suffer from chronic and/or severe headaches that seriously interfere with their lives.

All told, headaches account for 80 million of all doctors' office visits and more than 400...