The drug watchdog in the United States, the Food and Drug Administration (FDA), has expressed concerns regarding the anti-smoking drug Chantix.
The concerns come in the form of an 'early communication' about the drug and warns of reports of erratic behaviour in some taking Chantix.
An 'early communication' represents an ongoing safety review and reflects the FDA's current analysis of available data concerning drugs.
It does not in itself mean that FDA has decided that there is a relationship between the drug and the emerging safety issue but rather that the agency is evaluating post-marketing adverse event reports about a drug.
Chantix (varenicline), is a prescription medicine designed to help adults stop smoking, and the warning comes as a result of the FDA's request for information from Pfizer for adverse reports.
The company submitted reports to the agency describing suicidal thoughts and erratic behavior in an individual who had used Chantix, along with at least one death potentially linked to the medication.
The FDA has asked the company for any information on additional cases that may be similar in patients who have taken the drug.
When the FDA's Center for Drug Evaluation and Research completes their analysis of the available information and data, it says the conclusions and recommendations will be communicated to the public.
For now the FDA advises doctors to closely monitor patients taking Chantix for behavior and mood changes in patients within days to weeks of starting treatment.
Patients taking Chantix are advised to contact their doctors if they experience behavior or mood changes.
The FDA also advises patients to use caution when driving or operating machinery until they know how using Chantix may affect them.
Many drugmakers say the FDA is toughening up its stance on safety following the 2004 debacle over Merck's arthritis drug, Vioxx, and recent safety concerns about the diabetes drug, Avandia, produced by GlaxoSmithKline.
Some analysts suspect the FDA is being overly safety conscious because of such cases.
Pfizer says adverse event reports following a drug's approval are voluntarily submitted to companies by consumers and doctors and are a very sketchy indicator of any potential trends.
Pfizer is the world's biggest pharmaceutical company and Chantix apparently earned the company $241 million in the third quarter of 2007.