updated 6/4/2009 5:05:41 PM ET 2009-06-04T21:05:41

Federal regulators are still investigating the safety of Pfizer's anti-smoking drug Chantix, a probe that began last year after thousands of patients reported blackouts and other problems.

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Chantix was among the 20 medications under investigation for potential safety issues, according to an updated list from the Food and Drug Administration released Thursday.

The FDA is investigating reports of injury, visual impairment and other problems connected with Chantix, which is designed to help smokers quit.

Pfizer said it's continuing to track side effects with the medication. "As with all our medicines, we work with the FDA to ensure our labeling reflects the latest safety information," Sally Beatty, a spokeswoman for the New York-based company, said in a statement.

Regulators first began investigating Chantix in 2007 after receiving several reports of psychiatric problems, including suicidal thoughts. That prompted Pfizer to update the drug's labeling that patients should be monitored for unusual behavior.

The agency last fall began looking into scores of patient reports about blackouts and injuries while taking Chantix. A nonprofit group highlighted 1,001 reports to the FDA of serious injuries linked to the drug over a three-month period, more than for the 10 best-selling brand name drugs combined. Pfizer said at the time that the high number of reports might be linked to greater publicity about the side effects.

The Federal Aviation Administration later banned use of Chantix by pilots and air traffic controllers.

Current warnings on the drug say patients may be too impaired to drive or operate heavy machinery, but such language is standard for many medications.

The FDA began publishing quarterly lists of drugs under investigation last year to give consumers and doctors early notice about emerging safety issues. Drugs on the list have a "potential safety issue," but have not necessarily been directly linked to a problem.

Other popular drugs under FDA investigation include the sleeping disorder drugs Provigil and Nuvigil, from Cephalon. The agency is monitoring reports of skin reactions with the drugs.

A representative from Frazer, Pa.-based Cephalon did not immediately return a call for comment Thursday afternoon.

First approved in May 2006, Chantix quickly became one of the fastest growing products on Pfizer's balance sheet, though sales fell 4 percent last year to $846 million.

The twice-daily pill acts on nicotine receptors in the brain to block the pleasurable effects of nicotine and help patients quit smoking.

Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.


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