Washington ? A tablet shown to help more than one in five smokers quit joined the limited number of effective stop-smoking drugs on Thursday, approved by federal regulators.

When varenicline goes on sale later this year, it will become the first new prescription drug for smoking cessation approved by the Food and Drug Administration in nearly a decade and only the second stop-smoking drug that is nicotine-free, according to Pfizer Inc.

The New York company plans to market the twice-daily tablet, intended for adults only, 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 over and over 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 then rebranded as Zyban, an anti-smoking drug.

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

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