March 10, 2015 -- The FDA has changed the labeling on the quit-smoking drug Chantix to reflect concerns that it may lower your tolerance to alcohol and is linked to a rare risk of seizures.

"Until patients know how Chantix affects their ability to tolerate alcohol, they should decrease the amount of alcohol they drink. Patients who have a seizure while taking Chantix should stop the medicine and seek medical attention immediately," the FDA warns in a news release.

The new labeling is based on information submitted by Chantix maker Pfizer and on cases in the FDA Adverse Event Reporting System database.

Some people who drank alcohol during treatment with Chantix had increased drunkenness and unusual or aggressive behavior, or had memory loss.

The FDA says it also reviewed the database and medical literature for cases of seizures with Chantix. It found cases in which the people who had seizures while taking Chantix either had no history of them or had a seizure disorder that had been well-controlled.

"In most of these cases, the seizures occurred within the first month of starting Chantix. Information about these risks has been added to the Warnings and Precautions section of the drug label and to the patient Medication Guide," the FDA says.

The Warnings and Precautions section of the label has also been updated to include information about several studies that looked into the risk for certain side effects on mood, behavior, or thinking that happened with Chantix.

While the studies didn't show an increased risk of such side effects, “not all types of neuropsychiatric side effects were examined, and the studies had limitations that prevented the FDA from drawing reliable conclusions,” the agency says.

The FDA also says in its news release that it sent previous alerts about such potential side effects with Chantix in 2009 and 2011. Recent studies on the possibility of these kinds of side effects were discussed at an FDA Advisory Committee meeting in October 2014.

In 2009, the FDA began requiring a “black box warning” on Chantix warning of behavior changes including “hostility, agitation, depressed mood, and suicidal thoughts or actions.”

The FDA says Pfizer is doing a large safety trial of Chantix to investigate this risk. Results from this study are expected in late 2015.