WASHINGTON (AP) — A Pfizer drug shown to help more than one in five smokers quit after a year's use received federal approval on Thursday, adding another option to the limited pool of effective stop-smoking prescription medicines.

Varenicline is only the second nicotine-free smoking cessation drug to gain Food and Drug Administration approval. Pfizer Inc. plans to market the twice-daily tablet as Chantix.

"It's a welcome new addition. It's like with cancer or heart disease or high blood pressure or diabetes: the more effective treatments you have, the better off patients are," said Dr. Steven Schroeder, a professor of medicine at the University of California, San Francisco, who is active in smoking cessation efforts.

Varenicline works in two ways, by cutting the pleasure of smoking and reducing the withdrawal symptoms that lead smokers to light up again and again.

Most other stop-smoking drugs are various nicotine-replacement therapies, sold by prescription and over the counter in gum, patch, lozenge, nasal spray or inhaler form. In 1997, the FDA approved bupropion, an antidepressant already sold as Wellbutrin but rebranded it as Zyban, an anti-smoking drug.

Several studies conducted in Europe on about 2,000 smokers and presented in November at an American Heart Association conference showed that a year after initial treatment with varenicline, abstinence rates were 22%, vs. 16% among those given Zyban. Just 8% of those given dummy medicines had stopped after a year.

The approved course of Chantix treatment is 12 weeks, a length of time that can be doubled in patients who successfully quit to increase the likelihood they will remain smoke-free, the FDA said.

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