Disease of cerealgrasses, especially rye, caused by the fungusClaviceps purpurea. An ear of rye infected with ergot exudes a sweet, yellowish mucus. Ergot is the source of drugs used to control postpartum hemorrhage and to treat migraine headaches. Lysergic acid, from which the powerful hallucinogenLSD is synthesized, comes from ergot. Taking an overdose of ergot-derived medications or eating flour milled from ergot-infected rye can cause ergotism (also called St. Anthony's Fire) in humans and livestock; symptoms may include convulsions, miscarriages in females, and dry gangrene, and may result in death.