Ergot, which is caused by the fungus Claviceps purpurea, is a plant disease that affects cereal crops and grasseses such as rye, triticale, wheat and barley. It does not often affect oats.

The disease causes a reduction in the yield and quality of grain and hay produced, and if infected grain or hay is fed to livestock it causes a disease called Ergotism.

The disease cycle of the ergot fungus was first described in the 1800s, but the connection with ergot and epidemics among people and animals was known several hundred years before that.

Human poisoning due to the consumption of rye bread made from ergot infected grain was common in Europe in the Middle Ages.

Many ergot alkaloids, such as ergine, ergonovine and lysergic acid hydroxyethylamide have a poisonous hallucinogenic effect on the central nervous system, as they heavily interfere with neurotransmitter function.

Among those who studied ergot and its derivatives was Albert Hofmann whose experiments let to the discovery of LSD, an ergot derivative that strongly interferes with the neurotransmitter Serotonin.