Nicotine. Molecular graphic of nicotine, an addictive alkaloid drug found in tobacco. Nicotine (formula: C10.H14.N2) is an oily, colourless liquid. Atoms are here represented as sticks, and are colour-coded: carbon (white), nitrogen (grey) and hydrogen (orange). Nicotine is the active component of tobacco. In small doses, it stimulates the autonomic nervous system, but tolerance builds up fast, leading to addiction. As well as the toxic effects of nicotine, smoking tobacco can lead to serious lung problems, including lung cancer.