Headache is a very common medical symptom affecting 91% of males and 96% of females at some point during their lifetime. Some headaches are symptomatic of an underlying problem such as an infection, a hangover, a head injury, or a brain tumor. The International Classification of Headache Disorders, second edition (ICHD-II), defines these as “secondary headaches” because they are attributable to an underlying cause. The majority of headaches are benign and not attributable to an underlying cause. This group, referred to as primary headache disorders, includes migraine, tension-type headache, and cluster headache, among other disorders.