There is a general consensus that smoking is harmful to health and that tobacco contains a variety of harmful ingredients from which people who quit can benefit regardless of the circumstances. However, for long-term smokers, that is, people with tobacco dependence, sudden quitting may produce harm and risk of adverse symptoms. The most common symptoms include the following: 1. increased appetite, insomnia, anxiety, difficulty concentrating, restlessness, and irritability. 2. significant weight gain, usually 1-2 kg in the first two weeks after quitting. This is partly due to an increase in appetite and caloric intake, and partly due to a decrease in metabolic rate and an increase in lipoprotein synthesis. 3. Although all of the above symptoms may occur when you suddenly quit smoking, the total benefits of quitting are greater than the risks associated with the above in the long run, so it is necessary to quit smoking no matter how.