The red flags are flying all over the place, even over generics: A new study in the journal Neurology shows that verapamil, a drug for cluster headaches, can cause heart problems. At the least, verapamil patients should have frequent EKGs to check for irregular heartbeat. Sold under brand names Isoptin, Verelan, Calan, and Bosoptin, verapamil is a calcium-channel blocker also used to treat high blood pressure and angina. But the Neurology study only focused on patients using verapamil for cluster headaches. It found that 19 percent had irregular heartbeats and 12 percent had first-degree heart block; one patient had to get a pacemaker. The problems increased as dosage increased. Report