"My bet is that it will work as well as they do and, from the look of things, a little bit better," he said. The FDA does not recommend that Chantix be used with any other stop-smoking drug.

Varenicline latches on to the same receptors in the brain that nicotine binds to when inhaled in cigarette smoke, an action that leads to the release of dopamine in the pleasure centers of the brain. Taking the drug blocks any inhaled nicotine from reinforcing that effect. Its most common side effect is nausea.

The drug also slows the release of dopamine, thereby cutting the craving to smoke that occurs when nicotine's effect wears off, said Pfizer research chemist Jothan Coe, who invented the drug.

"It's a shield and at the same time, it stabilizes you and prevents you from having the lows, which lead to craving and withdrawal, but at the same time, it shields you from the highs," said Coe, a former 2 1/2 pack-a-day smoker who quit smoking the first time cold turkey and then a second time with the help of nicotine gum.

One in five American adults, or nearly 45 million people, smoke. An estimated 32 million of those smokers would like to quit, according to the Centers for Disease Control and Prevention. Smoking kills nearly 440,000 Americans a year.

"Tobacco use, particularly cigarette smoking, is the single most preventable cause of death in the United States and is responsible for a growing list of cancers, as well as chronic diseases including those of the lung and heart," said Dr. Scott Gottlieb, the FDA's Deputy Commissioner for Medical and Scientific Affairs.

Fewer than one in 20 smokers can quit without help, said Schroeder of UC San Francisco. Even with help, whether it's a drug, counseling or both, the success rate rises at most to roughly one in five, he added.

Both the FDA and European regulators recently rejected applications by Sanofi-Aventis to gain approval for rimonabant, or Accomplia, as a stop-smoking aid. Both have recommended that the drug, which blocks the same pleasure centers in the body activated when pot smokers get the munchies, be approved for weight loss.

And at least two vaccines are being developed that could block nicotine from ever reaching the brain.

Pfizer wouldn't say what Chantix will cost. The company had predicted annual sales of $1 billion, but analyst Barbara Ryan at Deutsche Bank is predicting $500 million in annual sales by 2009.

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Contributing: Theresa Agovino