The Food and Drug Administration yesterday approved the first birth control pill that eliminates a woman's monthly period.

Taken daily, the contraceptive, called Lybrel, continuously administers slightly lower doses of the same hormones in many standard birth control pills to suppress menstruation. It is designed for women who find their periods too painful, unpleasant or inconvenient and want to be free of them.

"This will be the first and only oral contraceptive designed to be taken 365 days a year, allowing women to put their periods on hold," said Amy Marren of Wyeth Pharmaceuticals, which expects Lybrel to be available with a prescription by July. "There are a lot of women who think that's a great option to have."

Company studies involving more than 2,400 women showed that Lybrel is as effective at preventing pregnancy as standard birth control pills and that it completely suppresses menstruation for many women within the first year, although some experience sporadic bleeding, the FDA said.

Advocates of birth control welcomed Lybrel, saying it provides women with another option.

"Every woman's birth control needs are different, and the best methods are those that fit a woman's lifestyle and meet her needs," said Vanessa Cullins, vice president for medical affairs at the Planned Parenthood Federation of America.

But others questioned whether enough research had been done to be sure that Lybrel is safe to suppress menstruation in the long term.

"There may be important health consequences that we don't know about," said Christine L. Hitchcock, an endocrinology researcher at the University of British Columbia. "I don't think we understand everything that the menstrual cycle does well enough to say with confidence that you can abolish it and not have any consequences."

Some criticized Lybrel for fueling biases and misconceptions about menstruation.

"I think it sends the wrong message about menstruation in women's lives, especially for young women," said Ingrid Johnston-Robledo, an associate professor of psychology and women's studies at the State University of New York at Fredonia. "It perpetuates a lot of negative attitudes and taboos about menstruation -- that it's something that's bothersome and dirty and debilitating and shameful."

Wyeth and the FDA said that there is no evidence of any long-term risks and that suppressing the menstrual cycle can have many benefits, especially for women who experience cramps, bloating and mood swings. There is no reason to think it would pose any additional health hazards, they said.

"The risks of using Lybrel are similar to other conventional oral contraceptives," said Daniel Shames, deputy director of the FDA's Center for Drug Evaluation and Research. "We don't suspect there are going to be any surprises in terms of long-term use of this product."