The author of a study on a widely-used drug that helps smokers quit is calling on the FDA to take the medication off the market.
Chantix is prescribed more than any other drug for those trying to stop smoking and the new study found it may be linked to heart problems.
That study released on Monday in a Canadian Medical Journal claims smokers who used Chantix had more cardiovascular problems than smokers who did not.
The drug's maker, Pfizer, said in a statement to ABC News that it disagrees with the study's conclusion and that the actual number of heart attacks and other cardiac events was too small to determine if Chantix was the cause.
Chantix has been prescribed to 13 million people.