What are the stages of nicotine addiction and briefly describe each of them.

There are three stages of nicotine addiction:
• first – episodic smoking of not more than 5 cigarettes per day; smoking cessation at this stage does not cause any disorders; small changes occurring in the activity of the nervous system are completely reversible at this stage;
• the second – constant smoking from 5 to 15 cigarettes per day; a slight physical dependence appears; upon cessation of smoking, a condition develops that is severe in physical and mental terms, it is removed only by smoking another cigarette;
• the third – constant smoking from one to one and a half packs per day; a habit of smoking on an empty stomach is developed, immediately after eating and in the middle of the night; addiction to tobacco is very strong; smoking cessation causes a serious condition of the smoker; pronounced changes in the nervous system and internal organs.