NEW YORK (CNNMoney.com) -- The FDA told Wyeth that it's going to have to do some more work on an experimental birth control drug before getting the green light from regulators, said the drugmaker on Wednesday.

Wyeth (up $0.60 to $42.97, Charts) said it received a letter from the Food and Drug Administration on Tuesday requesting more information on Lybrel, a once-a-day birth control pill. This is not the same thing as getting a drug approved by the FDA, because it adds extra steps to the review process and is not a guarantee.

Dr. Amy Marren, director of medical affairs for Wyeth, said the FDA wants assurance that Lybrel's packaging "is manufactured properly so that it is has the shelf life that we say it has." Also, Marren said the FDA wants to hold a public meeting, so that experts can present their views on Lybrel.

Wyeth did not provide a projected launch date for Lybrel, partly because a date for the public meeting has not been set.

Lybrel, if approved, would be the first birth control pill that is active every day of the year, said Wyeth. Current birth control pills are cyclical, alternating active drugs with placebos in accordance with the menstrual cycle.

David Moskowitz, analyst for Friedman, Billings & Ramsey, projects that Lybrel's annual sales will peak at $400 million in 2009, assuming the drug is approved.

Wyeth, based in Madison, N.J., said the Lybrel letter is not related to a recent warning letter from the FDA about a manufacturing plant in Puerto Rico.

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