Overuse of OTCs (over the counter medications) may result in chronic daily headache. Some believe that the most common form of headache is "Transformed Migraine". The individual may have started out with migraine, periodic headaches with symptom free episodes. However by taking OTCs and narcotics, endorphins are suppressed and the period headaches are gradually changed to chronic daily headaches. Therapy is aimed at strict reduction and limitation of analgesic therapy with attempts at prevention with prophylactic anti-migrainous drugs.  Head injury or previous subarachnoid hemorrhage may transform rare periodic migraine into chronic daily headache.  See Therapy for Chronic Daily Headache in the section on Prevention.