A dose the size of a few grains of table salt can kill an adult human. 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. Oral exposure to ricin is far less toxic and a lethal dose can be up to 30–40 milligrams per kilogram.
Ricin prevents cells from assembling various amino acids into proteins, and death occurs after a few hours up to a day. Ricin has been used as a terrorist weapon, including the assassination of Georgi Markov in 1978, supposedly by the KGB.
- "What makes ricin so deadly". Anthony Sabella. Retrieved 2013-04-24.
- "EFSA Scientific Opinion: Ricin (from Ricinus communis) as undesirable substances in animal feed  - Scientific Opinion of the Panel on Contaminants in the Food Chain". Efsa.europa.eu. Retrieved 2010-09-01.