Strychnine drug molecule. Molecular model of strychnine, an alkaloid drug that is used medicinally in low doses but which is also used as a poison for rats and other vermin. Strychnine has a chemical formula of C21H22N2O2, and occurs as colourless or white crystals. It acts as a nerve stimulant or tonic. High doses lead to convulsions, whilst death can be caused by the paralysis of the brain's respiratory centre. It is obtained commercially from plants of the Strychnus genus, especially from Nux vomica seeds. Atoms are colour-coded: carbon (grey), hydrogen (white), nitrogen (blue) and oxygen (red).