Smokers using the prescription drug Chantix (varenicline) to help them through the quitting process may want to sip their beers slowly, as this week the FDA approved new warnings that the drug can change the way users react to alcohol.

“Until patients know how Chantix affects their ability to tolerate alcohol, they should decrease the amount of alcohol they drink,” warns the FDA, which also issued a secondary Chantix-related warning that “Patients who have a seizure while taking Chantix should stop the medicine and seek medical attention immediately.”

According to the FDA, a review of data from Chantix maker Pfizer and of incidents in the agency’s Adverse Event Reporting System (FAERS) database found that “Some patients experienced decreased tolerance to alcohol, including increased drunkenness, unusual or aggressive behavior, or they had no memory of things that happened.”

Since 2006, the FDA knows of 11 cases of decreased tolerance to alcohol and 37 instances of alcohol-related aggressive behavior in Chantix patients.

In the tolerance instances, the patients said they did not consume an excessive almost of alcohol and that they had, before Chantix, been able to drink the same amount without adverse effects.

One patient was arrested following a motor vehicle accident, while a second “experienced a significant facial injury.”

In the cases involving aggressive behavior, patients said they had not consumed enough alcohol to explain their actions.

“In more than half of these cases, the patients described their behavior as a significant change from their behavior prior to Chantix treatment,” writes the FDA, which says that 22 of the 37 cases involved harm to a person or property.

There were also reports of amnesia following alcohol ingestion in patients taking Chantix. Nearly half of the aggressive behavior cases reported no memory or impaired memory of their experience.

The agency also looked at Chantix users who experienced seizures without any prior history of seizure or whose seizure disorders had previously been well-controlled.

“In most of these cases, the seizures occurred within the first month of starting Chantix,” reports the FDA, which says the median time to seizure onset was 2-3 weeks after beginning treatment with the drug.

The agency is also in the process of reviewing studies claiming to dispel previously issued warnings about Chantix that patients may experience adverse neuropsychiatric side effects including suicidal thoughts. Research recently provided to the FDA finds no increased risk of these side effects, but the agency contends that the studies only look at certain types of neuropsychiatric side effects, namely those that require hospitalization.

Later this year, Pfizer is expected to submit the results of a large clinical safety trial of Chantix.

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