Nicotine
Nicotine is a highly addictive substance poured out from the tobacco plant.
The addiction of nicotine is physical and mental both. The addict of nicotine starts craving for the substance and they constantly desire for the nicotine effects, because inhaling tobacco smoke is one of the fastest ways to get any drug to your nervous system as it goes directly into your brain.
People who have depression, schizophrenia, post-traumatic stress disorder or some other sort of mental Illness are more prone to be smokers. Consumption of nicotine causes neurons to release excess dopamine, which makes people relaxed. But the good feeling doesn't last long, so people crave for another cigarette to feel good. People also become habituated to intake of tobacco in particular situations, such as after meals, while driving, with friends or during coffee breaks.
Tobacco is very dangerous. It contains more than 60 cancer-causing chemicals and other harmful substances. The diseases that are caused by using tobacco are; lung cancer, heart disease, eye problems, osteoporosis, asthma, infertility and impotence, leukaemia etc.