Chantix acts at sites in the brain affected by nicotine. The FDA says the drug may help some smokers quit by providing some nicotine effects to reduce the craving and withdrawal symptoms and by blocking the effects of nicotine from cigarettes if people resume smoking. Reducing the enjoyment from smoking could help break the cycle of nicotine addiction.

The FDA approved the twice-a-day Chantix pill based on data that included late-stage clinical trials involving more than 2,000 smokers. On average, they had smoked about 21 cigarettes per day for an average of 25 years.

In two studies, patients who took Chantix for 12 weeks "nearly quadrupled the likelihood of quitting than those taking placebo," Pfizer said. Chantrix users also "had nearly twice the likelihood of quitting" than patients taking buproprion, which is sold under the brand name Zyban by GlaxoSmithKline (GSK - commentary - Cramer's Take).

Patients in the clinical trials received educational materials and were followed for 40 weeks after treatment. After one year, approximately 20% of Chantix users had stopped smoking. "For those patients who quit at the end of 12 weeks, an additional course of 12 weeks treatment with Chantix resulted in a greater likelihood of long-term success in quitting smoking," Pfizer said.

The major side effects detected in clinical trials included nausea, changes in dreaming, constipation, gas and vomiting.