Nicotine: An alkaloid (a nitrogen-containing chemical) made by the tobacco plant or produced synthetically. Nicotine has powerful pharmacologic effects (including increased heart rate, heart stroke volume, and oxygen consumption by the heart muscle), as well as powerful psychodynamic effects (such as euphoria, increased alertness, and a sense of relaxation). Nicotine is also powerfully addictive.

An alkaloid, which is the major psychoactive substance in tobacco. It has both stimulant and relaxing effects. It produces an alerting effect on the electroencephalogram and, in some individuals, an increased capacity to focus attention. In others, it reduces anxiety and irritability. Nicotine is used in the form of inhaled tobacco smoke, "smokeless tobacco" (such as chewing tobacco), snuff, or nicotine gum. Each puff of inhaled tobacco smoke contains nicotine that is rapidly absorbed through the lungs and delivered to the brain within seconds. Considerable tolerance and dependence develop to nicotine. Because of its rapid metabolism, brain levels of nicotine fall rapidly and the smoker experiences craving for a further cigarette 30-40 minutes after finishing the last one (WHO Lexicon of alcohol and drug terms).

WHO ICD-11 6C4A Disorders due to use of nicotine - Disorders due to use of nicotine are characterised by the pattern and consequences of nicotine use. Nicotine is the active dependence-producing constituent of the tobacco plant, Nicotiana tabacum. Nicotine is used overwhelmingly through smoking cigarettes. Increasingly, it is also used in electronic cigarettes that vaporize nicotine dissolved in a carrier solvent for inhalation (i.e., “vaping”). Pipe smoking, chewing tobacco and inhaling snuff are minor forms of use. Nicotine is a highly potent addictive compound and is the third most common psychoactive substance used worldwide after caffeine and alcohol. Nicotine Dependence and Nicotine Withdrawal are well described and Nicotine-Induced Mental Disorders are recognized. 

WHO ICD-11 6C4A.3 Nicotine intoxication - Nicotine intoxication is a clinically significant transient condition that develops during or shortly after the consumption of nicotine that is characterised by disturbances in consciousness, cognition, perception, affect, behaviour, or coordination. These disturbances are caused by the known pharmacological effects of nicotine and their intensity is closely related to the amount of nicotine consumed. They are time-limited and abate as nicotine is cleared from the body. Presenting features may include restlessness, psychomotor agitation, anxiety, cold sweats, headache, insomnia, palpitations, paresthesias, nausea or vomiting, abdominal cramps, confusion, bizarre dreams, burning sensations in the mouth, and salivation. In rare instances, paranoid ideation, perceptual disturbances, convulsions or coma may occur. Nicotine intoxication occurs more commonly in naïve (non-tolerant) users or among those taking higher than accustomed doses.

WHO ICD-11 QE12 Hazardous nicotine use - A pattern of nicotine use that appreciably increases the risk of harmful physical or mental health consequences to the user or to others to an extent that warrants attention and advice from health professionals. Most often nicotine is consumed in the form of tobacco, but there are also other forms of nicotine delivery (e.g., nicotine vapour). Hazardous nicotine use has not yet reached the level of having caused harm to physical or mental health of the user or others around the user. The pattern of nicotine use often persists in spite of awareness of increased risk of harm to the user or to others. This category is not intended to include the use of nicotine replacement therapies under medical supervision when these are used as part of attempts to stop or reduce smoking.