So many smokers try to quit. Many turn to a drug called Chantix to reduce those health risks. But doctors disagree on whether the risks outweigh the benefits.
"Chantix is the worst drug on the U.S. Market," says Curt Furberg, M.D.
Researchers pooled data on 14 studies of Chantix. They found smokers who take the drug have a 72% increased chance of serious heart problems like heart attack.
"We had smokers without any evidence of heart disease and this was... where we found substantial increase risk of cardiac events," said Sonal Singh, M.D. with the Johns Hopkins University School of Medicine.
But some doctors say if you only look at the 72% increase number, you'll miss the bigger picture: the total number of cardiac events in the studies was quite small. Just over 1% of people on Chantix.
Other experts help put the differing views of the new numbers into perspective:
"it doesn't mean that there's nothing there. But it means that whatever risk seems to be there is very small," says Raymond Niaura, Ph.D. with the American Legacy Foundation.
Pfizer markets Chantix, and in a statement, said it's working with the FDA "to review and monitor data for Chantix."
Pfizer had previously agreed to put a heart warning on the drug's label for patients already suffering from heart disease.
While the numbers can get hazy -- one thing is clear -- smokers can improve their health if they're able to kick their habit.
Chantix has been on the market since 2006. After three months of use, up to half of users stop smoking at least temporarily.