Doctors with the Federal Aviation Administration (FAA) have added a new warning for users of the anti-impotence drug Viagra. CBS News Correspondent Dan Raviv reports that for airline pilots, Viagra can blur "the wild blue yonder."

Shortly after Viagra's release, some users reported blue-tinted vision after taking the pill. The warning to the pilots from the FAA doctors says Viagra may impair pilots' ability to distinguish between blue and green, important for runway lights and instrument panels.

The FAA officials say flight doctors are being urged to tell pilots not to fly within six hours after a dose of the impotency treatment drug.

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Writing in the fall edition of the Federal Air Surgeon's Medical Bulletin, Dr. Donato Borolo said that "although only 3 percent of all patients report visual disturbances, this blue-green impairment could be dangerous" while flying at night or in bad weather.

"The correct identification by the pilot of blue and green is necessary for safe flight. In addition, the use of color video terminal displays has increased in aviation and may present a problem in the color-deficient pilot."

The FAA doctors also delicately list another side effect as "cockpit distraction" because of "an activity not condoned by the FAA, but known to occur." It warns that "[Viagra] use by a pilot with cardiac disease during sexual intercourse at 5,000 feet could be deadly."

In an interview with The Dallas Morning News, American Airlines spokesman John Hotrod said he's not aware of Viagra use as an issue for the airline's pilots.

"I'm not sure there are that many who would admit they needed it," Hotrod told the newspaper.

Dr. Warren Silberman, the FAA doctor who manages the government's flight-physical program, said he knew of no accidents or incidents attributable to the little blue pills.

"But," he said, "we have had a tremendous number of pilots and medical examiners calling in and asking, 'What about Viagra?'"

The answer, Dr. Silberman said, is a simple motto: "Six hours from Viagra to throttle."

