A new birth control pill that can stop menstruation forever? Yes, the FDA approved such a pill last week, the first time it's taken such an action.

Here are some key issues to consider:

Q: What is this new pill?

A: It's a slightly lower dose of the same hormones - progesterone and estrogen - contained in most regular birth control pills. It's called Lybrel and made by Wyeth Pharmaceuticals.

Q: How does it work?

A: It's taken once a day 365 days a year.

Q: What do doctors say?

A: "For women with such painful periods that they're laid up for days, or patients who have severe anemia and heavy periods, it makes sense," says Dr. Paul Norris, assistant professor of obstetrics and gynecology at the University of Miami School of Medicine.

Q: What do women say?

A: Many are cautiously optimistic. "Where you can avoid debilitating cramps, it's a great idea," says Dr. Judith Horowitz, a Coral Springs psychologist and fertility expert. "For work productivity, it should be excellent."

Q: Is it safe never to menstruate?

A: Yes, say most doctors. When menstruation occurs, the uterus sloughs off its endometrium, the layer of cells that has been building up to facilitate implantation of sperm needed for conception. When your period ends, the process starts over. But when you're on the new pill, the endometrium is suppressed, so menstruation isn't necessary. "Studies, even biopsies, have shown that it's safe," Norris says.

Q: What about long-term use?

A: Doctors for years have been telling patients with debilitating periods to stay on their regular birth-control pills without taking a week off for menstruation, said Dr. Guillermo Lievano, an obstetrician/gynecologist at Baptist Hospital.

Q: Is there a downside?

A: The biggest is that women in the clinical trial of the new pill had breakthrough bleeding and spotting, says Wyeth spokesperson Natalie De Vane. It happened more in the first three to six months, tapering off after a year. Of 2,400 patients in the Wyeth study, 56.8 percent dropped out, and for 18 percent, the reason was the bleeding.

That displeases Dr. Jerilynn Prior, of the Centre for Menstrual Cycle Research in Vancouver. "So women have to trade the expected for the unexpected," she says. "It's a wicked trade-off."

Q: Will taking Lybrel interfere with later returning to a regular menstrual cycle or becoming pregnant?

A: Wyeth says no.

Q: What about future studies?

A: Wyeth will conduct ongoing studies, De Vane says, particularly of any possibility of blood clots.

With all oral contraceptives based on progesterone and estrogen, the risk of a blood clot is about 1 in 10,000; the risk of heart attacks or stroke is about 1 in 100,000, Norris says.

Q: Are there women who shouldn't take Lybrel?

A: Women should avoid it if they have had a heart attack or stroke, blood clots, some cancers, liver disease, unexplained vaginal bleeding or who might become pregnant, Wyeth says.

Q: What if you become pregnant accidentally?

A: "The danger is that you might keep taking the pills through the early stages of pregnancy," says Judy Norsigian, executive director of Our Bodies, Ourselves, formerly the Boston Women's Health Collective - which has published eight versions of its popular book by that title since 1970.

"That might harm the fetus," she says. "This is the problem with drugs getting on the market before long-term studies are done."