The FDA approved a new migraine drug on Thursday. Aimovig, known generically as erenumab, is the first drug shown to stop migraine headaches before they start. The drug would be approved for patients who have tried other drugs and found no relief. In studies, it did not entirely prevent migraines, but reduced their frequency. FDA's approval means the drug may soon be available under prescription. It should also be paid for by health insurance. The drug's maker, Amgen, said U.S.