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Harvard Commentaries
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Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School


The Addiction


April 17, 2012

Tobacco Cessation
22017
Basics
The Addiction
The Addiction
SmokingStep2Piece4
Quitting is far more than just a mental battle. The nicotine in cigarettes creates a physical addiction.
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InteliHealth
2012-04-17
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InteliHealth Medical Content
2015-04-23

Reviewed by the Faculty of Harvard Medical School

 

You've taken on a challenging goal. As you struggle to quit smoking, you may think you lack willpower or discipline. But this is not the case.

Quitting is far more than just a mental battle. The nicotine in cigarettes creates a physical addiction. In fact, the U.S. Surgeon General declared nicotine an addictive drug in 1989. Because nicotine is legal and easily available, people in the United States abuse nicotine more than any other drug.

How Nicotine Addiction Works

Nicotine is the main ingredient in most forms of tobacco, including cigarettes, cigars, pipe tobacco and chewing tobacco. Nicotine is either inhaled through the lungs or absorbed through the cells that line the mouth and nose. It then enters the bloodstream and travels throughout the body, where it has several effects:

  • In the brain, nicotine triggers the release of dopamine, a neurotransmitter (brain hormone) that contributes to feelings of pleasure. (Cocaine produces a similar chemical effect.)

  • Also in the brain, nicotine serves as a stimulant, increasing the brain's electrical activity.

  • In the adrenal cortex, a gland near the kidney, nicotine triggers the release of adrenaline (epinephrine), which stimulates the central nervous system.

These stimulant effects occur almost immediately after tobacco use. For example, nicotine reaches your brain within 10 seconds after you smoke a cigarette.

At the same time, the stimulant effect of nicotine from a single cigarette does not last long. When the nicotine effect wears off, you may experience withdrawal symptoms, such as depression and fatigue. Tobacco users thus crave more nicotine to avoid these sedative effects. This cyclical behavior can ultimately lead to an addiction to nicotine.

Nicotine addiction takes months to develop. It does not occur the first time you smoke a cigarette, but rather builds over time.

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Tolerance And Dependence

In people who smoke on a regular basis, the stimulant effects of chronic nicotine use can persist up to 24 hours a day. Eventually, a tolerance to nicotine develops, and the body requires more and more nicotine to achieve these same effects. In other words, to get the same high or buzz, you need to start smoking more cigarettes.

During sleep, the level of tolerance diminishes, because the levels of nicotine in the blood decline. Many smokers find the first cigarette of the day to be the "best" because they are replenishing their low nicotine levels. As smoking continues throughout the day, tolerance again increases, and cigarettes smoked later in the day have fewer stimulant effects.

There are many other toxic substances in cigarettes, including carbon monoxide and tar, but only nicotine has this addictive quality.

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A Sobering Fact

Each cigarette contains about 10 milligrams of nicotine, of which one to two milligrams are absorbed directly into the bloodstream. If absorbed all at once, a couple of grams of pure nicotine could kill a healthy person. Since your body breaks down nicotine at a rapid pace, and a cigarette is smoked over time, the levels in your system never get this high.

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