Ricin

Ricin ( /ˈraɪsɪn/), from the castor oil plant Ricinus communis, is a highly toxic, naturally occurring protein. A dose as small as a few grains of salt can kill an adult human. The LD₅₀ of ricin is around 22 micrograms per kilogram (1.76 mg for an average adult, around 1⁄₂₂₈ of a standard aspirin tablet/0.4 g gross) in humans if exposure is from injection or inhalation. Oral exposure to ricin is far less toxic and a lethal dose can be up to 20–30 milligrams per kilogram.