In May, the Food and Drug Administration approved varenicline (Chantix), a nicotine-free pill, to help stop cigarette smoking. Here's some background to help you decide if this drug is right for you.

Varenicline proved only modestly effective in clinical trials. In two large trials, the smoking cessation rates after one year in men and women who smoked about one pack of cigarettes a day were 22 percent for varenicline, 16 percent for bupropion (Zyban), another approved smoking cessation drug, and 10 percent for those taking a placebo.

Even though this success rate may appear modest, varenicline was apparently approved because of the great need for effective ways to get people to stop smoking. Varenicline also works differently from other drugs available to help smokers quit.

When nicotine binds to its receptor in the brain, the release of large amounts of dopamine produces the pleasurable sensations of smoking. Varenicline works by binding to the nicotine receptor first, thus blocking nicotine from binding to it and releasing dopamine.

Like bupropion pills and nicotine gum, patches, sprays, and inhalers, varenicline also reduces the unpleasant withdrawal symptoms that follow smoking cessation.

Taken twice daily, varencline's major side effect in clinical trials was mild nausea. The FDA approved varencline use for a 12-week period with the option to continue for an additional 12 weeks if the drug has proven effective. The FDA does not recommend the use of varencline in combination with other antismoking products.