Called Lybrel, it's the first such pill to receive Food and Drug Administration approval for continuous use. When taken daily, the pill can halt women's menstrual periods indefinitely and prevent pregnancies.

It's the latest approved oral contraceptive to depart from the 21-days-on, seven-days-off regimen that had been standard since birth-control pill sales began in the 1960s. The Wyeth pill is the first designed to put off periods altogether when taken without break.

The FDA planned a late-afternoon news conference to announce approval.

Wyeth plans to start Lybrel sales in July. The Madison, N.J., company said it hasn't yet determined a price. The pill contains a low dose of two hormones already widely used in birth-control pills, ethinyl estradiol and levonorgestrel.

Most of the roughly 12 million U.S. women who take birth-control pills do so to prevent pregnancy. Others rely on hormonal contraceptives to curb acne or regulate their monthly periods.

Some nontraditional pills such as Yaz and Loestrin 24 shorten monthly periods to three days or less. Seasonique, an updated version of Seasonale, reduces them to four times a year. With Lybrel, in tests, 59 percent of women who took the medication had no bleeding after six months.