The most important toxic substances in tobacco leaves are tar and carbon monoxide. Nitrosamine and benzoquinone are the two most carcinogenic substances in tar. Most of the people killed by smoking die from nitrosamines and benzoquinones. Lung cancer. According to the World Health Organization, smoking is the first preventable cause of morbidity and mortality. Therefore, smoking cessation has always been the focus of global health. A small amount of nicotine does not directly harm the human body. Clinical studies have shown that nicotine is expected to be an effective drug for the treatment of Alzheimer's disease, Parkinson's disease and depression. At the same time, nicotine is not only found in tobacco leaves, but also in the fruits of various Solanaceae plants. For example, plants such as tomatoes and scorpions contain nicotine, which is recognized as beneficial to humans. Healthy food, if nicotine is really harmful, then I am afraid that people who have eaten tomatoes have been poisoned. Because of this, the World Health Organization promoted “nicotine replacement therapy” globally in the 1990s to replace smoking, replacing nicotine that was previously obtained from cigarettes, helping people to physically and psychologically overcome their dependence on cigarettes. The chances of success in quitting smoking have more than doubled.