Strychnine is a poison with several medicinal effects. It is most commonly used as a poison for small mammals. Strychnine has the chemical formula C₂₁H₂₂N₂O₂ and it is the principal alkaloid found in the seeds from plants in the Strychnos family, including Strychnos nux- vomica (Quaker buttons or poison nut). Strychnine can account for 5% of the weight of the nuts of this tree, which is a native of Indian and Malaysia. When concentrated it can be crystalized out into colorless prisms with a melting point of 520^oF (270^oC). Strychnine has a stimulatory effect on all parts of the nervous system and in large doses it can produce convulsions and death. The senses are made more acute and blood pressure increases whilst the heart rate decreases, it can be effectively used for heart failure. Strychnine is used as a poison for rats and other vermin, it is particularly effective in this role due to the rapidity with which it is absorbed.

Strychnine is odorless but it has a very bitter taste. Medicinally it has been used to cure constipation, to stimulate the appetite, and in cases of heart failure.