Chantix (varenicline), a prescription medication used to help patients stop smoking, may cause or exacerbate psychiatric illness, according to a Public Health Advisory issued by the U.S. Food and Drug Administration (FDA). The FDA is advising consumers to tell their health care provider about any history of psychiatric illness prior to starting Chantix, because Chantix may cause worsening of current psychiatric illness -- even if that illness is currently under control -- and may also cause an old psychiatric illness to reoccur. According to the FDA, 37 suicides and more than 400 cases of suicidal behavior have been linked to Chantix. The Associated Press reports that in November, the FDA "began investigating reports of depression, agitation and suicidal behavior among patients taking the popular twice-daily pill." Chantix is manufactured by Pfizer and was approved by the FDA in May 2006.