HOOKED ON NICOTINE.

IF SMOKING IS SO BAD, WHY DO SMOKERS KEEP REACHING FOR MORE? THEY'RE ...

Like 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 (see "Anatomy of a Smoker," p. 9). 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 percent 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.

SMOKE SIGNALS

Not every smoker is addicted to nicotine, About one in 10 is an occasional smoker, who 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 (see p. 10).

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.

WHAT A DRAG!

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.

UP IN SMOKE

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 yom' 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, therapy that helps smokers control the way they respond to cravings. Best prevention: Don't even start!

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RELATED ARTICLE: Anatomy of a Smoker

Cigarette smoke pollutes every part of a smoker's body, causing short- and long-term destruction. Here's a look inside.

POOR TEETH

Tar--the dark, sticky mixture of chemicals in cigarette smoke--makes a smoker's teeth yellow. Smoke also inhibits antibodies that protect your gums from periodontal disease, which leads to receding gums and tooth loss.

SORE THROAT 

Smoking thickens the lining of the throat, and can lead to throat cancer.

DAMAGED LUNGS

Smoking stunts the growth of teens' lungs and decreases their breathing capacity. As the lungs try to protect themselves from inhaled smoke, the bronchial lining thickens. This process can lead to lung cancer.

STAINED FINGERS

Smoking causes fingernails and fingertips to turn yellow.

A TOXIC CLOUD

Secondhand smoke is more chemically polluted than inhaled smoke. Nonsmokers inhaling secondhand smoke can suffer from watery eyes, headaches, and allergic reactions. Secondhand smoke has also been linked to cancer in nonsmokers.

REDUCED FERTILITY

Smoking reduces fertility in both men and women. Pregnant smokers risk miscarriage, and their babies may suffer from premature birth.

BAD BLOOD

Carbon monoxide in cigarettes reduces up to 12 percent the amount of oxygen normally carried by red blood cells. Less oxygen makes breathing and physical activity difficult. Smoking also raises blood pressure 10 to 15 percent, increasing the risk of stroke.

DRUGGED BRAIN

Nicotine enters the brain only eight seconds, after a smoker inhales. Like cocaine, heroin, and other drugs of abuse, nicotine enters the part of the brain that regulates reward and pleasure signals.

RUINED SKIN

Smoking destroys elastin, the elastic fibers that keep skin smooth and wrinkle-free. It also constricts blood vessels near the skin's surface. Result: early wrinkles.

STRESSED HEART

Smoking increases the heart rate by 10 to 25 beats a minute. Smokers have a greater risk of irregular heart beat and heart attack.