Pfizer's Chantix, a smoking-cessation drug, carries a risk of major adverse cardiovascular event, the U.S. Food and Drug Administration said in a statement.

Chantix (varenicline) is a medicine (used by prescription) that helps people quit smoking. The drug works by blocking the effects of nicotine in the brain. About 1.26 million patients in the U.S. have received Chantix prescription, says FDA. Chantix increases the likelihood of abstinence from smoking for as long as a year.

The agency, after a meta-analysis of studies conducted on the effects of the drug, concluded that there was a higher occurrence of major adverse cardiovascular events in people who used Chantix than in people who were on placebo.

The meta-analysis included data obtained from 7,000 patients; 4190 of which were on Chantix. These people were part of 15 studies sponsored by Pfizer and had received treatments for 12 weeks or more. The study analysis found that there was a risk for cardiovascular events, but it wasn't statistically significant.

FDA has advised healthcare professionals to weigh in the risks and benefits associated with using the drug in helping people quit smoking. FDA maintains that smoking is a major risk factor in heart related complication and quitting smoking has immediate and substantial benefits.

Patients who use Chantix and have been diagnosed with heart disease are advised to contact their physicians if they find their symptoms of cardiovascular disease worsening over time. Symptoms include chest pain, shortness of breath, calf pain when walking, or sudden onset of weakness, numbness, or difficulty speaking.

"The benefits of quitting smoking are immediate and substantial. Chantix has been demonstrated to increase the likelihood of abstinence from smoking for as long as one year compared to treatment with placebo," MacKay Jimeson, a spokesman for Pfizer, told Bloomberg in an e-mail.