Knowing about potential risks now, he said, he probably would have done more research, consulted more doctors and tried means of quitting that didn't involve the "wonder drug" first.

Others might also be seeking alternatives, despite such testimonials about effectiveness. Pfizer reported revenue of $199 million in the first quarter of the year from Chantix, up 5 percent, largely because of international sales. But the company said sales were tempered by labeling in the United States. France also has stopped covering the drug, called Champix in Europe, under its public insurance.

Pfizer says doctors have written 7 million prescriptions for Chantix in the United States and 13 million worldwide since it was approved in 2006. It had a shortened review period because the FDA said it had shown a significant improvement over available therapy.

Singh said he and colleagues from Wake Forest University School of Medicine and the University of East Anglia in the United Kingdom decided to take a closer look at Chantix when one of the doctors reported patients with chest pains.

With a grant from the National Institutes of Health's National Center for Research Resources and the NIH Roadmap for Medical Research, they reviewed 14 clinical trials involving 8,200 healthy people who took Chantix or a placebo. Singh said the extent of the risk for heart attacks and arrhythmias wasn't apparent until all the data were reviewed at once.

There weren't a large number of deaths, according to the study, but the risk for those without heart disease having a cardiac event that required hospitalization was 72 percent higher than for those taking a placebo. The average age of study participants was less than 45.

Singh estimated there have been 62,000 serious cardiac events in the United States from the drug. He now emphasizes the need to quit smoking, but without Chantix.

The FDA says smoking kills 1,200 people a day. The American Heart Association calls it the most preventable cause of premature death in the country. It can lead to several chronic diseases including cancer, lung problems and coronary artery disease.

The association supports both drugs and counseling to help tobacco users quit, as does the U.S. Preventive Services Task Force, an independent panel of prevention experts. Approved drugs include over-the-counter nicotine patches, gum and lozenges, and a prescription nicotine-replacement product, Nicotrol.

Chantix and Zyban, or bupropion, are non-nicotine, prescription pills. Zyban also carries an FDA warning about possible psychiatric problems.

"Combination therapy with counseling and medications is more effective than either component alone," the task force recommendation reads.

As part of the campaign against smoking, the federal government is turning to new graphic packaging on cigarettes. And states such as Maryland are maintaining free phone lines.

The state established the Tobacco Quitline, 1-800-QUIT-NOW, in 2006 and also offers free nicotine replacement therapy to callers who register for counseling, said Dawn S. Berkowitz, chief of the state's division of federal and special tobacco control initiatives.

The state reports the percentage of residents who smoke dropped to 15.2 percent in 2010 from 20.5 percent in 2000, and among high school students, the rate dropped to 14.1 percent in 2010 from 23 percent in 2000.

Singh said he encourages his patients to quit through counseling and maybe nicotine patches. He plans to continue lobbying the FDA to increase the warnings for, and insurance companies to no longer fund, Chantix.

"Patients ask for Chantix because the ads are all over TV," he said. "If they say they want to quit smoking, I'll spend time and counsel them. … There are too many consequences from this drug."