The addictive effects of tobacco
The main reason why tobacco becomes addictive is due to the content of Nicotine, which alters brain functioning. Most smokers continue to smoke in order to avoid the pain of withdrawal symptoms Addiction to tobacco (nicotine) is not immediate. It may take weeks or months to develop. For those who smoke more than 15 cigarettes per day, there remains a high level of Nicotine in the blood, which makes quitting difficult.
Stopping can produce unpleasant withdrawal symptoms including depression, insomnia, irritability, difficulty concentrating, restlessness, anxiety, decreased heart rate, increased appetite, weight gain, and craving for nicotine. Symptoms peak from 24 to 48 hours after stopping and can last from three days up to four weeks, although the craving for a cigarette can last for months.