FRIDAY, Aug. 13 (HealthDay News) -- The U.S. Food and Drug Administration on Friday approved the ella (ulipristal acetate) emergency contraceptive pill, which prevents pregnancy if taken within five days of unprotected intercourse or contraceptive failure.

The prescription-only drug, which has been available in Europe since May 2009, is a progesterone agonist/antagonist that is thought to work by inhibiting or delaying ovulation, according to a statement from the FDA.

Approval comes after an agency advisory committee unanimously supported ella's approval in a decision announced in June.

"The safety and efficacy of ella were demonstrated in two phase [3] clinical trials," the FDA noted. "One study was a prospective, multi-center, open-label, single-arm trial conducted in the United States; the other was a randomized, multi-center, single-blind comparator-controlled trial conducted in the United States, United Kingdom and Ireland."

The agency said that side effects noted with ella are similar to those of other emergency contraceptives already approved and include headache, abdominal pain, nausea, pain/discomfort during menstruation (dysmenorrhea), fatigue and dizziness. The drug, manufactured by Paris-based Laboratoire HRA Pharma, is not recommended for women who are pregnant or think they might be pregnant or for women who are breast-feeding.

Planned Parenthood was quick to commend the FDA's decision.

"Every woman deserves every option available to prevent an unplanned pregnancy, and there are many reasons why a woman may face the risk of unintended pregnancy, from failure or improper use of birth control to sexual assault," Cecile Richards, the group's president, said in a statement. "The FDA's approval of this new form of emergency contraception gives women one more option."

But ella has its detractors, as well. Experts believe the drug works by delaying the ability of the ovaries to produce an egg. However, opponents note that progesterone is also required to help the womb prepare for an already fertilized egg -- raising the possibility that the drug works similarly to RU-486, which prevents a fertilized egg from implantation in the womb.

"Ella is an abortion drug," Wendy Wright, president of Concerned Women for America, told the Washington Post. "It operates the same way as RU-486 -- the abortion drug. Many women may be comfortable taking a contraceptive but would object to taking an abortion drug."

But ella's proponents dismiss those charges, saying that there's no data to support the notion that the drug works as anything but a contraceptive.

More information

For a look at ella's labeling, head to the FDA.