Nicotine, a naturally occurring constituent of tobacco, is the addictive, active ingredient in tobacco smoke. Although nicotine is highly toxic—it is used as an insecticide, fumigant, and vermifuge and in large doses can cause respiratory paralysis and even death in humans—the amount inhaled when smoking a cigarette is relatively small, about 3 mg. Depending on how it is inhaled, nicotine can act as a stimulant or as a tranquilizer. What is a lethal dose of nicotine for humans? Discuss