The United States has approved an oral contraceptive that will also put an indefinite stop to women's monthly periods.

On Tuesday, the Food and Drug Administration, gave the okay to Lybrel for continuous use.

The drug is not yet approved, however, in Canada.

Wyeth, the U.S. pharmaceutical company that developed Lybrel, plans to start sales in the U.S. in July, it said.

The pill contains low doses of two hormones already in use in the current generation of birth-control pills: ethinyl estradiol and levonorgestrel.

About 12 million women in the U.S. take birth control pills. Most do so to prevent pregnancy, but some rely on them to curb acne or regulate their monthly periods.

There are some pills such as Yaz and Loestrin 24 that can shorten monthly periods to three days or less. Seasonique can reduce them to four times per year.

Tests of Lybrel show that 59 per cent of women who took the drug had no bleeding after six months.

However, Wyeth said about 18 per cent of women dropped out of studies because they encountered spotting and breakthrough bleeding -- a problem of low-dose pills.

Not for everyone

Because of the bleeding encountered by women who have used the pill, the FDA is not recommending the pill should be used by all women using birth control.

"You take it every single day and you don't get your period," Dr. Marla Shapiro told CTV's Canada AM. "From a medical point of view and an evidence-based medical point of view, there is really no reason that women necessarily need to have a period."

It would be most beneficial to women who would prefer not to have their periods because they suffer from menstrual cramps, heavy menstrual bleeding, anemia and menstrual migraines.

"There is a subset of women to who this birth control pill is a welcome alternative. " Shapiro said.

Women should be advised that Lybrel will have some of the same side effects as a regular birth control pill and that unscheduled or irregular bleeding is also a possibility.

Jean Elson, a sociology professor at the University of New Hampshire, has mixed feelings about the pill.

"I certainly believe that for women who have extraordinary menstrual cycles, women who have excruciating pain who are hemorrhaging during their menstrual cycles that this is very important for them," Elson said.

"However, I am concerned that this may be advertised as a kind of a magic pill which is a cure-all for all women who have menstrual cycles and who might have much more minor problems and think that this may be a way to avoid them."

Some experts argue that reformulating birth control pills to have them manage periods detracts from their original purpose.

As hormone levels have fallen in birth-control pills, failure rates have increased.

The FDA is considering whether to set an acceptable failure rate for the pills. A panel of advisers told the agency that less effective birth-control pills should still be improved if they provide other benefits such as improved safety.

Lower-dose birth control pills reduce the risk of potentially deadly side effects such as blood clots and stroke.

With files from The Associated Press