In 2016, the FDA revised its warnings on varenicline to clarify that the risk of serious side effects on mood, behavior, or thinking were lower that they had thought, and that the benefits of quitting smoking outweigh any risk associated with varenicline.
However, if you experience agitation, hostility, depressed mood, changes in behavior or thinking, or if you develop suicidal thoughts or behavior, immediately stop taking varenicline and contact a healthcare professional.
Medical review: Nathan Cobb, MD, September 26, 2017
US Food and Drug Administration. FDA revises description of mental health side effects of the stop-smoking medicines Chantix (varenicline) and Zyban (bupropion) to reflect clinical trial findings. 12/16/2016.