Nicotine dependence is a state of dependence upon nicotine. Nicotine dependence is a chronic, relapsing disease defined as a compulsive craving to use the drug, despite social consequences, loss of control over drug intake,  and emergence of withdrawal symptoms. Tolerance is another component of drug dependence. Nicotine dependence develops over time as a person continues to use nicotine. The most commonly used tobacco product is cigarettes, but all forms of tobacco use and e-cigarette use can cause dependence. Nicotine dependence is a serious public health problem because it leads to continued tobacco use, which is one of the leading preventable causes of death worldwide, causing more than 8 million deaths per year.According to the World Health Organization, "Greater nicotine dependence has been shown to be associated with lower motivation to quit, difficulty in trying to quit, and failure to quit, as well as with smoking the first cigarette earlier in the day and smoking more cigarettes per day." The WHO estimates that there are 1.1 billion smokers globally. Of the 34 million smokers in the US in 2018, 74.6% smoked every day, indicating the potential for some level of nicotine dependence. There is an increased frequency of nicotine dependence in people with anxiety disorders.There are different ways of measuring nicotine dependence.
Repeated exposure to nicotine can cause an increase in the number of nicotinic receptors, which is believed to be a result of receptor desensitization and subsequent receptor upregulation. This upregulation or increase in the number of nicotinic receptors significantly alters the functioning of the brain reward system. With constant use of nicotine, tolerance occurs at least partially as a result of the development of new nicotinic acetylcholine receptors in the brain. After several months of nicotine abstinence, the number of receptors go back to normal. Nicotine also stimulates nicotinic acetylcholine receptors in the adrenal medulla, resulting in increased levels of adrenaline and beta-endorphin. Its physiological effects stem from the stimulation of nicotinic acetylcholine receptors, which are located throughout the central and peripheral nervous systems. Chronic nicotinic acetylcholine receptor activation from repeated nicotine exposure can induce strong effects on the brain, including changes in the brains physiology, that result from the stimulation of regions of the brain associated with reward, pleasure, and anxiety. These complex effects of nicotine on the brain are still not well understood.When these receptors are not occupied by nicotine, they are believed to produce withdrawal symptoms. These symptoms can include cravings for nicotine, anger, irritability, anxiety, depression, impatience, trouble sleeping, restlessness, hunger, weight gain, and difficulty concentrating.Neuroplasticity within the brains reward system occurs as a result of long-term nicotine use, leading to nicotine dependence. There are genetic risk factors for developing dependence.