Nicotine

Columbus brought tobacco back to Europe from America in the late fifteenth century. When tobacco smoke is inhaled, nicotine is absorbed through the lungs, and reaches the brain in about 7 seconds. Nicotine works by mimicking the actions of a naturally occurring brain chemical, acetylcholine, by docking with its special receptor molecules. Some of these nicotine receptors in the brain activate part of the 'pleasure centre', which could be responsible for nicotine's euphoric effects.