Reports made to the FDA and to Chantix manufacturer Pfizer include cases of patients who became more inebriated than usual, were uncharacteristically aggressive and had blacked out after drinking.
"Until patients know how Chantix affects their ability to tolerate alcohol, they should decrease the amount of alcohol they drink," the FDA said in a statement issued this week.
The agency also said that there have been "rare accounts" of seizures in patients taking Chantix. Some of these patients had seizure disorders that were previously under control; others had no history of seizures.
Details about both of these side effects have been added to the Chantix drug label as "Warnings and Precautions."
About 1.2 million people filled prescriptions for Chantix in 2013, according to data from IMS Health. The pill, whose generic name is varenicline, attaches itself to nicotine receptors in the brain so that they can't be stimulated by the nicotine in cigarettes. That way, if a patient has a momentary lapse and lights up, the experience won't be satisfying. Chantix also prompts the brain to release small amounts of dopamine, which helps alleviate symptoms of nicotine withdrawal. According to Pfizer, the most common side effects are nausea, trouble sleeping, and gastrointestinal problems like gas and constipation.
Compared with a placebo, Chantix nearly tripled smokers' odds of success, according to a 2013 Cochrane Library review. That study also found that Chantix was 51% more effective than a nicotine patch and 72% more effective than nicotine gum.
Since 2006, the FDA has received 11 reports of "decreased tolerance for alcohol" in people who were consuming amounts of alcohol that had never caused them trouble before they started taking Chantix. At least some of these events had serious consequences. In one case, a Chantix patient wound up with a "significant facial injury," according to the FDA's Adverse Event Reporting System. In another case, a patient caused a motor vehicle accident and was arrested by police.
The FDA also received 37 reports of aggressive behavior after drinking only a small amount of alcohol, including 22 incidents that resulted in "harm to a person or property." In 16 cases, Chantix patients had "no memory or impaired memory of their experience." Several patients also told Pfizer that they had memory problems after mixing Chantix and alcohol.
On its Chantix website, Pfizer echoes the FDA's advice to limit drinking until patients see how they tolerate alcohol while taking the smoking cessation drug. The company also acknowledges that Chantix users have "had changes in behavior, hostility, agitation, depressed mood, [and] suicidal thoughts or actions." Patients experiencing any of these problems should stop taking the medication and call their doctors right away, Pfizer said.
Regarding seizures, the FDA said it was aware of 64 cases, including 37 in people who had never had seizures before. In 10 of those cases, the only risk factor for seizures was Chantix, according to the FDA. Typically, the first seizure occurred two to three weeks after patients began taking Chantix, the agency said.
The FDA also addressed concerns that Chantix may cause neuropsychiatric side effects, including suicidal thoughts. This possibility was raised by the FDA in 2009, but studies conducted since then have not shown a conclusive link. Pfizer is conducting a clinical trial to find some answers, and the results are expected to be available later this year, the FDA said.