Nicotine

Effects on the body

In small doses nicotine has a stimulating effect, increasing activity, alertness and memory. Repeat users report a pleasant relaxing effect. It also increases the heart rate and blood pressure and reduces the appetite. In large doses it may cause vomiting and nausea. The LD50 of nicotine (that is, the lethal dosage reported to kill 50% of the population) is 50 mg/kg for rats and 3 mg/kg for mice. 40-60 mg can be a lethal dosage for adult human beings.

Related Topics:
Heart - Blood pressure - Vomit - Nausea - LD - Rat - Mice

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Repeat users of nicotine often develop a physical dependency to the chemical. A report released on May 16, 1988 by United States Surgeon General C. Everett Koop stated that the addictive properties of nicotine are similar to those of heroin and cocaine; although many people do not agree with such a comparison.

Related Topics:
May 16 - 1988 - United States Surgeon General - C. Everett Koop - Addictive - Heroin - Cocaine

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Physical withdrawal symptoms include irritability, headaches, anxiety, cognitive disturbances and sleep disruption. These symptoms peak at around 48-72 hours, and generally cease after two to six weeks.

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Although the amount of nicotine inhaled with tobacco smoke is quite small (most of the substance is destroyed by the heat) it is still sufficient to cause dependence. The amount of nicotine absorbed by the body from smoking depends on many factors, including the type of tobacco, whether the smoke is inhaled, and whether a filter is used. For chewing tobacco, which is held in the mouth between the cheek and gum, the amount released into the body tends to be much greater than smoked tobacco.

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As nicotine enters the body, it quickly gets distributed through the bloodstream and can cross the blood-brain barrier. On average it takes about seven seconds for the substance to reach the brain. It acts on the nicotinic acetylcholine receptors. In small concentrations it increases the activity of these receptors, among other things leading to an increased flow of adrenaline, a stimulating hormone. The release of adrenaline causes an increase in heart rate, blood pressure and respiration, as well as higher glucose levels in the blood. Cotinine is a break-down product of nicotine which remains in the blood for up to 48 hours, and so can be used as an indicator of a person's exposure to smoke. In high doses, nicotine blocks the nicotinic acetylcholine receptor, which is the reason for its toxicity and its effectiveness as an insecticide.

Related Topics:
Bloodstream - Blood-brain barrier - Brain - Nicotinic acetylcholine receptor - Adrenaline - Hormone - Glucose - Cotinine - Toxicity - Insecticide

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In addition, nicotine increases dopamine levels in the reward circuits of the brain. Studies have shown that smoking tobacco inhibits monoamine oxidase (MAO), an enzyme responsible for breaking down monoaminergic neurotransmitters such as dopamine, in the brain. It is currently believed that nicotine by itself does not inhibit the production of monoamine oxidase (MAO), but that other ingredients in inhaled tobacco smoke are believed to be responsible for this activity. In this way, it generates feelings of pleasure. This reaction is similar to that caused by cocaine and heroin, and is another reason people keep smoking: to sustain high dopamine levels.

Related Topics:
Dopamine - Brain - Monoamine oxidase - Enzyme - Monoaminergic neurotransmitters - Cocaine - Heroin

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It has been noted that the majority of people diagnosed with schizophrenia smoke tobacco. Estimates for the number of schizophrenics that smoke range from 75% to 90%. It is argued that the increased level of smoking in schizophrenia may be due to a desire to self-medicate with nicotine. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12084420

Related Topics:
Schizophrenia - Self-medicate

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http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7864277

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Nicotine and its metabolites are being researched for the treatment of a number of disorders, including ADHD, Parkinson's Disease and Alzheimer's Disease.

Related Topics:
ADHD - Parkinson's Disease - Alzheimer's

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The carcinogenic properties of nicotine in stadalone form, i.e. separate from tobacco smoke, have not been evaluated by the IARC, and it has not been assigned to an official carcinogen group. The currently available data indicates that nicotine on its own does not promote the development of cancer in healthy tissue, and has no mutagenic properties. Its teratogenic properties have not yet been adequately researched, and while the likelihood of birth defects caused by nicotine is believed to be very small or nonexistent, nicotine replacement product manufacturers recommend consultation with a physician before using a nicotine patch or nicotine gum while pregnant or nursing. However, nicotine and the increased acetylcholinic activity it causes have been shown to impede apoptosis, which is one of the means used by the body to destroy unwanted cells (programmed cell death). Since apoptosis helps remove mutated or damaged cells that may evolve into cancerous tissue, its inhibition by nicotine creates more favourable conditions for cancer to develop once the initial mutations have occurred. Thus, in combination with the numerous potent carcinogens in tobacco smoke, nicotine plays a role in carcinogenesis and may be considered to be a carcinogen on those grounds. It is also important to note that its addictive properties are often the primary motivating factor for tobacco smoking, contributing to the proliferation of cancer.

Related Topics:
Carcinogen - IARC - Cancer - Mutagen - Teratogenic - Nicotine patch - Nicotine gum - Apoptosis - Programmed cell death - Carcinogenesis - Tobacco smoking

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