Ergot poisoning is a rare form of toxic reaction to exposure to the ergot fungus, which is the source of lysergic acid diethylamide or LSD. It is currently very rare, but was more common in centuries past (where it was often mistaken for demonic possession) as the ergot fungus grows well on grain, particularly rye, which is kept in moist conditions. The fungus is not destroyed by milling or cooking (although it is destroyed by refining), so cooked whole grain products can also be contaminated.