Understanding Plan B: How Emergency Contraception Separates Itself From Routine Birth Control, Prevents Pregnancy

Emergency contraception is exactly how it sounds: it’s a method of contraception women can take after having unprotected sex. You most likely refer to it as the morning-after pill or just “Plan B,” which is short for the leading brand Plan B One-Step. But how exactly does the pill work to prevent pregnancy? What sets it apart from routine birth control? And is it the same as having an abortion?

Here’s what we know.

Pregnancy Isn’t Instantaneous

Getting pregnant isn’t something that happens during or right after sex — a necessary reminder provided the current state of sex education. Sperm can survive for several days in a woman’s body, so depending on when the woman ovulates, it can actually take up to six days for the sperm and egg to meet after you have sex, Dr. Raegan McDonald-Mosley, chief medical officer for Planned Parenthood Federation of America (PPFA), told Medical Daily in an email.

“That’s why it's possible to prevent pregnancy even after you have sex,” she said.

If women don't wish to get pregnant after having had, or being forced to have unprotected sex, there are three emergency methods to consider: levonorgestrel pills (Plan B and Next Choice One Dose), ulipristal acetate pills (Ella), and a copper ParaGard intrauterine device (IUD). Levonorgestrel is a progestin, which is a synthetic progestogen that mimics the hormone progesterone. Progesterone is the female hormone that works to prevent changes in a woman’s uterus.

It’s been used in birth control pills for several decades, Denise Bradley, senior vice president of Global Corporate Reputation at Teva Pharmaceuticals, told Medical Daily in an email; Teva is responsible for Plan B. Progestin pills work mainly by stopping the release of an egg from the ovary. Plan B in particular, Bradley said, has a higher dose of progestin, but it works similar to other pills taken to prevent pregnancy. Bradley added Plan B may also work by preventing fertilization of an egg or by preventing attachment to the uterus.

The IUD, on the other hand, works a little differently. It affects the way the sperm move so they can't join with an egg, Mosley explained. As you know, if sperm can’t join with an egg, women can't get pregnant.

'It's Worth Taking'

The image below charts how effective each method of emergency contraception is, courtesy of Planned Parenthood.

As you can see, the IUD ranks as the most effective with its 99.9 percent effective rate, followed by Plan B’s 89 percent rate and Ella’s 85 percent rate. Women who choose the IUD are then in a position to use this method as their routine form of birth control; it can effectively prevent pregnancy for up to 12 years.

Ella is the one method of emergency contraception not recommended for all women, namely for women who may be breastfeeding. Mosley said if women do take it, or perhaps have no other option, they should pump their breast milk and discard the milk for 36 hours after ingestion. Perhaps for this reason, Ella must be prescribed by a doctor or nurse, while most other brands, including Plan B, are now available over the counter without a prescription. IUDs must be inserted by your doctor or nurse.

It's important to know that these rates are contingent on both time and (possibly) a woman’s body mass index (BMI). Plan B is most effective when taken within three days after having unprotected sex, while Ella and an IUD are effective up to five days after having sex.

Less is known about ways in which weight influences contraceptions' efficacy rate. In 2013, the European company HRA Pharma actually changed the packaging of a pill similar to Plan B to say the product was ineffective for women who weighed more than 176 pounds. There are other experts who believe efficacy starts to wane at 165 pounds. Ella claims to be less effective for women with a BMI of 35, and Plan B claims to be less effective for women with a BMI over 25. To Aine Mac Grory, a pharmacist working in Northern Ireland, this is a “bold statement to make.”

“It’s a big asterisk,” she previously told Medical Daily. “I’ll give the morning-after pill to a heavier women, but I’ll tell her it may not give you the same effects. Take someone who is 9 stone (126 pounds) and someone who’s 15 stone (210 pounds). There is so much more body to get through. There’s a risk. I would let them know that.”

Mosley would agree with Mac Grory. “If the IUD or Ella aren’t options for you, it’s perfectly safe to take [Plan B] or [Next Choice]. It’s still worth taking," she said.

Regardless of which method women go with, they should take a pregnancy test two weeks after the fact to make sure they're not pregnant. If the test reads negative, but women are still worried they may be pregnant, Mosley suggests taking another test in a week. So, three weeks since initially taking emergency contraception, to be sure.

'So Safe and Effective'

There have been no reports of serious complications among the millions of women who have used the emergency contraception pill, Mosley said. But, as with most forms of birth control, there could be side effects, such as changes to your normal period, headaches, and nausea.

"It’s important to remember that if you vomit within three hours of taking [emergency contraceptive pills], you need to retake it, since it won’t be effective,” Mosley said. Women with preexisting medical conditions, such as asthma, diabetes, and hypertension should not be scared of having to take emergency contraception. Each method is perfectly safe for women to utilize, Mosley added.

“I especially recommend that women with medical problems seeking to avoid pregnancy and in need of emergency contraception consider the copper IUD because it is so safe and effective — both as emergency contraception and routine form of [birth control],” she said. One more thing women should not be worried about? Inducing an abortion.

The idea that emergency contraceptive pills equate to a medical abortion has persisted for years. The thing is, there's no scientifc proof of this. Susan Wood, the former assistant commissioner for women’s health at the FDA, ruled the morning-after pill is not an abortifacient. At the same time, a study published in the journal Contraception declared Plan B does not have an effect after ovulation. Colorado lawmakers are trying argue IUDs are an abortifacient, but science has yet to find that it is.

It's probably the most confusing aspect of emergency contraception. She herself has yet to come across evidence that any form of emergency contraception affects an existing pregnancy or would cause an abortion. The drugs women can take to actually induce an abortion contain mifepristone and misoprostol, which blocks progesterone so the uterus lining breaks down and empties. "Abortion pills" work only when a woman is already pregnant, Mosley said.

"Emergency contraception will not work if a woman is already pregnant,” she concluded. "[It] only works to prevent a pregnancy from occurring in the first place."