Nicotine. Computer graphic of a molecule of nico- tine, an addictive, poisonous alkaloid drug found in tobacco; it is also used as an insecticide. Nicotine (3-(1-methyl-2-pyrrolidyl)pyridine) is an oily, colourless liquid. It contains hydrogen (H), carbon (C) & nitrogen (N), and has the chemical formula C10H14N2. In small doses, nicotine stimulates the autonomic nervous system, promoting the flow of adrenaline and other internal secretions. In larger doses it paralyses the autonomic nervous system by preventing the transmission of nerve impulses across the spaces between adjoining nerve cells. Very large doses may cause convulsions and death.