Ricin

Ricin is a poison. It is a highly toxic, naturally occurring protein. It is produced in the seeds of the castor oil plant Ricinus communis.

A dose of ricin the size of a few grains of table salt can kill an adult human.^[1] The median lethal dose (LD₅₀) of ricin is around 22 micrograms per kilogram (1.78 mg for an average adult, around ​¹⁄₂₂₈ of a standard aspirin tablet/0.4 g gross) in humans if injected or inhaled.^[2] Oral exposure to ricin is far less toxic and a lethal dose can be up to 30–40 milligrams per kilogram.^[source?]

Ricin prevents cells from assembling various amino acids into proteins. Death can occur within a few hours or up to a day later.

Ricin has been used as a terrorist weapon, including the assassination of Georgi Markov in 1978, supposedly by the KGB.^[source?]