Rabbit anti-Ricinus communis Grain Ricin chain B polyclonal antibody for ELISA, WB, Neut. Ricin, 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. The LD50 of ricin is around 22 micrograms per kilogram (1.76mg for an average adult, around 1/228 of a standard aspirin tablet (0.4g gross)) in humans if exposure is from injection or inhalation. Oral exposure to ricin is far less toxic and lethal dose can be up to 20–30 milligrams per kilogram.