Cafergot is a combination of an ergot alkaloid (ergotamine tartrate) and a stimulant (caffeine). It is used to treat certain types of headaches (vascular headaches including migraine and cluster headaches). Headache pain can sometimes be caused by widened blood vessels in the head. Ergotamine works by narrowing these widened blood vessels. Caffeine increases the absorption of ergotamine and also narrows widened blood vessels.