The first birth-control pill meant to put a stop to women's monthly periods indefinitely has won U.S. government approval, the manufacturer said Tuesday.

Called Lybrel, it is 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 is 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 Pharmaceuticals pill is the first designed to put off periods altogether when taken without break.

The FDA planned a news conference to announce approval of a new contraceptive.

Wyeth plans to start Lybrel sales in July. The company said it has not yet determined its 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 the pill do so to prevent pregnancy. But others rely on hormonal contraceptives to curb acne or regulate their monthly periods. Other nontraditional pills like 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 it had no bleeding after six months.

However, 18 percent of women dropped out of studies because of spotting and breakthrough bleeding, according to Wyeth. That sort of unanticipated and irregular bleeding can be a problem with low-dose pills.

Still, a women's health expert said Lybrel would be a welcome addition for the woman who seeks relief from the headaches, tender breasts, cramps and nausea that can accompany her monthly periods.

"Over time she will experience markedly less bleeding episodes or no bleeding episodes. That is very beneficial for some women — and is wanted by some women," said Dr. Vanessa Cullins, vice president for medical affairs at Planned Parenthood Federation of America Inc.

University of New Hampshire sociologist Jean Elson recognized Lybrel's advantages for what she characterized as the small number of women who suffer extraordinarily during menstruation, but overall said the pill left her with mixed feelings.

"For women in that situation, I certainly can understand the benefits of taking these kinds of medications, but for most women menstruation is a normal life event — not a medical condition. Why medicate away a normal life event if we're not sure of the long-term effects?" said Elson, who researches the sociology of gender and medical sociology.

In recent years, as the hormone content of birth-control pills has dipped, failure rates have climbed. The FDA is mulling whether to establish an acceptable failure rate for the pills and, if so, what that rate should be. In January, a panel of agency advisers said less-effective birth-control pills should still merit federal approval if they promise other benefits, including improved safety.

Generally, lower-dose birth-control pills can reduce the risk of serious and sometimes deadly side effects, including blood clots and stroke, associated with their use.