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ashtrayLike every other teen, Brian Kennedy of New York City knew all about the dangers of cigarette smoking — the toll it takes on your lungs, heart, and the rest of your body. But that didn't stop him from lighting up his first cigarette when he was only 11.

Now at 17, Brian is struggling to kick a pack-a-day habit. How's it going? "It's kinda rocky," he admits. "Every once in a while I still give in." Brian knows why: He's addicted to nicotine — the primary chemical in tobacco that keeps a smoker reaching for more.

Brian is one of 35 million smokers who try to quit each year, according to the National Institute on Drug Abuse (NIDA). Less than 10% succeed without help. Now, scientists have begun to unlock the secrets behind addiction, whether to nicotine, marijuana, alcohol, or any other drug.

Research shows that nicotine, like other addictive drugs, affects the mesolimbic system — the part of the brain that produces "feel good" chemicals. One recent study zeroed in on a specific brain protein, called beta 2 subunit, that is essential to nicotine addiction. Without this protein in their brains, lab mice don't experience nicotine's pleasurable sensations. Result: They don't crave or get addicted to the drug. Scientists hope such studies can lead to better methods for treating nicotine addiction.

Not every smoker is addicted to nicotine. About one in 10 is an occasional smoker, can pass on a cigarette for days without suffering from withdrawal symptoms, like wrenching headaches or intense cravings. But the vast majority of smokers become hooked on nicotine. The key may lie in brain chemistry.

"When you smoke nicotine or any drug, for that matter, it reaches the brain in about eight seconds," explains Dr. Stephen Heishman, a NIDA researcher in Baltimore, Maryland. In the brain, nicotine stimulates the release of dopamine, a chemical or neurotransmitter that allows communication between nerve cells.

Dopamine transmits pleasure signals when you eat chocolate or receive a hug, for example. By releasing a cascade of dopamine in the brain, nicotine gives smokers that pleasurable feeling that makes them want more — and more.

Nicotine addiction is not instantaneous. "Addiction takes around two to three years — from the time a person first tries a cigarette to the point where he or she is smoking on a daily basis," Dr. Heishman says. In fact, the first drag often makes a new smoker dizzy and nauseous, thanks to nicotine's adverse effects.

Few people realize that pure nicotine is actually quite deadly. Nicotine is the active ingredient in some insecticides. "A couple of drops (about 60 milligrams) of pure nicotine would kill you," Dr. Heishman warns. For every cigarette a person smokes, he or she inhales about 1 to 3 mg of nicotine. Fortunately, the body quickly breaks down nicotine to keep it from building up to a fatal dose.

After repeated exposure to nicotine, your body gets used to the drug. The brain creates more receptors, the parts of a nerve cell to which nicotine and neurotransmitters bind. This process is part of why smokers get addicted. "With more receptors, you need more of a drug to occupy those receptors," Dr. Heishman says. That's what makes quitting so hard.

Strangely enough, nicotine is not what makes smoking so harmful. The real villain is the cigarette itself, which pumps more than 4,000 chemicals into your body, about 200 of which are poisonous. The damage that's done to the heart and lungs is primarily due to tars, carcinogens(cancer-causing chemicals), and carbon monoxide in smoke, Dr. Heishman explains.

Compared to a cigarette's other hazards, nicotine is fairly safe. That's why the Food and Drug Administration approved nicotine replacement therapy — nicotine gum and patches — to treat smokers. Both gum and patches deliver nicotine to the brain, but at a much slower rate than cigarettes. In patches, small doses of nicotine are released through the skin over a given period of time. While both alternatives can satisfy nicotine craving, they're less likely to lead to addiction.

The patch helped Brian avoid cigarettes the first week he quit. "The patch made it not as bad," he says.

Researchers are experimenting with other alternatives as well. ImmuLogic, a Massachusetts company, plans to test an anti-smoking vaccine on volunteers — smokers trying to kick the habit. The vaccine's antibodies (substances that destroy foreign matter in the body) seek out and neutralize nicotine before it reaches the brain's receptors. Smokers no longer get a "nicotine hit," so smoking loses its appeal.

Ultimately, the best treatment for quitting cigarettes may combine drugs that combat nicotine craving, and therapy that helps smokers control the way they respond to cravings. Best prevention: Don't even start!

By Maria L. Chang | December 14 , 1991

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