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Nicotine is an agonist at nicotinic acetylcholine receptor which are present in the central and autonomic nervous systems, and the neuromuscular junction. At low doses nicotine causes stimulatory effects on these receptors, however, higher doses or more sustained exposures can cause inhibitory effects leading to neuromuscular blockade. [4] [30]
Cotinine has an in vivo half-life of approximately 20 hours, and is typically detectable for several days (up to one week) after the use of tobacco. The level of cotinine in the blood, saliva, and urine is proportionate to the amount of exposure to tobacco smoke, so it is a valuable indicator of tobacco smoke exposure, including secondary (passive) smoke. [14]
Using nicotine products during cancer treatment may be contraindicated, as nicotine may promote tumour growth, but temporary use of NRTs to quit smoking may be advised for harm reduction. [ 76 ] Nicotine gum is contraindicated in individuals with temporomandibular joint disease . [ 77 ]
Between 1933 and the late 1940s, the yields from an average cigarette varied from 33 to 49 mg "tar" and from less than 1 to 3 mg nicotine. In the 1960s and 1970s, the average yield from cigarettes in Western Europe and the USA was around 16 mg tar and 1.5 mg nicotine per cigarette. Current average levels are lower. [4]
The probabilities of death from lung cancer before age 75 in the United Kingdom are 0.2% for men who never smoked (0.4% for women), 5.5% for male former smokers (2.6% in women), 15.9% for current male smokers (9.5% for women) and 24.4% for male "heavy smokers" defined as smoking more than 25 cigarettes per day (18.5% for women). [120]
Nicotine itself, however, is addictive but not otherwise very harmful, as shown by the long history of people safely using nicotine replacement therapy products (e.g., nicotine gum, nicotine patch). [13] Nicotine increases heart rate and blood pressure and has a range of local irritant effects but does not cause cancer. [14]
In nicotine-dependent smokers, quitting smoking can lead to nicotine withdrawal symptoms such as nicotine cravings, anxiety, irritability, depression, and weight gain. [23]: 2298 Professional smoking cessation support methods generally attempt to address nicotine withdrawal symptoms to help the person break free of nicotine addiction.
It may be decades before the long-term health effects of nicotine e-cigarette aerosol inhalation is known. [19] Short-term nicotine use excites the autonomic ganglia nerves and autonomic nerves, but chronic use seems to induce negative effects on endothelial cells. [20] Nicotine may result in neuroplasticity modifications in the brain. [21]