which are left at the discretion of the examiner. nih main article: nih classification of headaches the nih classification consists of brief definitions of a limited number of headaches. the nih system of classification is more succinct and only describes five categories of headaches. in this case, primary headaches are those that do not show organic or structural causes. according to this classification, primary headaches can only be vascular, myogenic, cervicogenic, traction, and inflammatory. management an old advertisement for a headache medicine