Caffeine is the most widely consumed psychostimulant drug. It is a potent antagonist of adenosine receptors at dosages consistent with common dietary intake. With infrequent exposure, caffeine may act as an analgesic for headache or an adjuvant for the actions of other analgesics. With chronic repetitive intake, caffeine is associated with an increased risk of development of analgesicoveruse headache, chronic daily headache and physical dependency. Cessation of caffeine use following chronic exposures leads to a withdrawal syndrome, with headache as a dominant symptom.