The active ingredient in the drug, to be sold under the brand name Chantix, "is a new molecular entity that received a priority FDA review because of its significant potential benefit to public health," the agency said Thursday.

Pfizer said Chantix, which it called Champix during development, is the first new prescription antismoking drug in nearly a decade. "Smoking harms nearly every organ in the body [and] is responsible for approximately one in five deaths in the U.S.," said Hank McKinnell, Pfizer's chairman and CEO. "This medical advance from Pfizer will now help many smokers end their addiction."

A Pfizer spokeswoman said the drug will be available during the second half of the year. Pfizer also has submitted a Chantix application to the European Union.

Chantix is the fourth new Pfizer drug to get FDA clearance this year. The others are Exubera, an inhaled insulin for diabetics, which should reach the U.S. market by midyear; the antifungal, Eraxis, for treating dangerous bloodstream infections; and Sutent, for the treating advanced kidney cancer and certain stomach cancer tumors.

In a few days, the company expects to hear from the FDA on Indiplon, an insomnia drug Pfizer has developed with Neurocrine Biosciences (NBIX - commentary - Cramer's Take). Pfizer also expects to hear from the FDA this year on it application for Zeven, an antibiotic.

Despite the news, Pfizer's stock was off 22 cents to $24.82 in late afternoon trading.

The FDA's decision "is a positive for Pfizer, although not of outsized consequence," says Chris Shibutani, of JP Morgan, in a Thursday research note. He predicts the drug could produce $320 million in U.S. sales by 2010, while foreign-market sales could add another $150 million.

Those numbers could be conservative, Shibutani says, because Pfizer hasn't revealed the drug's price. He has an outperform rating on the company. He doesn't own shares; his firm has had a recent investment banking relationship.

C. Anthony Butler, of Lehman Brothers, is more optimistic about Chantrix's prospects, telling clients in a Thursday report that worldwide sales could be "in the $1 billion range" by the end of 2010.

Although insurers may be wary about paying for stop-smoking drugs, Butler says they "might view the mid-to-long term savings garnered by reducing the healthcare costs associated with smoking as a beneficial tradeoff." Butler has an outperform rating on Pfizer. He doesn't own shares. His firm says it does and seeks to do business with companies covered in research reports.

The Centers for Disease Control and Prevention says an estimated 44.5 million adults in the U.S. smoke cigarettes, and more than 8.6 million of them have at least one serious illness caused by smoking. "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.