The US researchers on Wednesday revealed that hundreds of patients taking Pfizer Inc's anti-smoking drug Chantix have reported serious accidents, vision problems and heart trouble.

The study by researchers at the nonprofit Institute for Safe Medication Practices, and Wake Forest University, reported hundreds of reported problems since the drug's 2006 approval that included blurred vision, dizziness, confusion and loss of consciousness.

The researchers said, "These data provide a strong signal that the risks of varenicline treatment have been underestimated and show that a wide spectrum of serious injuries are being reported in large numbers.”

Responding to the study quickly, the Federal Aviation Administration on Wednesday announced that it would no longer permit pilots or air traffic controllers to use the smoking cessation drug Chantix, citing potential side effects that could pose a threat to the safe operation of aircraft.

Laura Brown, an F.A.A. spokeswoman stated that the agency had approved the use of Chantix for airline pilots and flight controllers last year, but was notifying 150 pilots and 30 air traffic controllers known to be using it that the drug was no longer acceptable and should be discontinued.

In February, the Food and Drug Administration had issued a public health advisory, saying that some Chantix users had developed a variety of serious psychiatric symptoms, and that some had committed suicide.

The researchers cautioned that the data does not definitively prove that Chantix is at fault but does indicate that the U.S. Food and Drug Administration and Pfizer should take further steps, including conducting more studies.

The New York City based drug maker, Pfizer, However defended Chantix, saying the side effects are already mentioned on the drug's label. Gretchen Dieck, Pfizer's senior vice president for safety and risk management, said, "When you've got the nicotine withdrawal along with Chantix, it's just very difficult to tell what is causing it.”

On the news, the shares of Pfizer fell to their lowest level since 1997.