Headaches at the back of your head that improve only when you take Cosart 25 usually mean your blood pressure is rising when you skip the medicine. Cosart helps control the pressure, so the pain goes away. If the headache keeps returning, you likely need regular BP control rather than taking it only sometimes. Try to check your BP at home, reduce salt, stay hydrated, and manage stress. It is best to talk to your doctor to adjust your BP medication so the headaches do not keep coming back.