You’re Screwed If You Wait Too Long to Take Plan B

The Scenario: Your friend calls you in a panic. She and her partner had a slip up: Things got hot and heavy, condoms were not in the mix, and bae thought his pull-out game was strong. (It was not.) With fear in her heart and semen dripping down her leg, your friend asks what she should do to make sure she isn't pregnant. You tell her to get Plan B, an emergency contraception she can pick up at the drugstore. She tells you you're a genius. But she clearly isn't because when you check on her two days later, she hasn't gotten the pill yet.

"Don't worry," she says. "I heard Plan B works for like, five days." You're pretty sure it needs to be taken within three days, plus you can't help but wonder: Doesn't it get less effective with every passing hour?

How it Works: Plan B One Step, a.k.a. "the morning-after pill," is a hormonal medication called levonorgestrel, and it's arguably one of the best known forms of emergency contraception available. It's not magic, though. "Essentially, taking levonorgestrel makes the body think it is pregnant already, and so it shouldn't release an egg from the ovary. If an egg is not released, it can't be fertilized by a sperm to create a pregnancy," says Eleanor Bimla Schwarz, a professor of medicine at University of California Davis Medical Center. You should also tell your friend that she can take the pill regardless of where she is in her cycle. There's no any harm to taking Plan B if a woman does not want to be pregnant but suspects she isn't ovulating at the time of the incident, Schwarz says. And for the record, the box says it should be used as directed within 72 hours (three days) of unprotected sex or birth control failure.

The Worst That Could Happen: Look, we don't want to make value-judgments about pregnancy. Babies are super cute and parenthood is probably lit, but if your friend called you frantically trying to avoid getting pregnant, we'd bet the worst that can happen as she takes her sweet time is: pregnancy. Research published by Pediatric Child Health shows that if Plan B is taken within 24 hours of unprotected sex (or birth control failure), the ability to prevent pregnancy is 95 percent, if taken between 25-48 hours after sex, that efficacy decreases to about 85 percent. And if taken between 48-72 hours after exposure to sperm, the effectiveness decreases to about 58 percent.

"The effectiveness [of Plan B] goes down with every day that passes because there's more time when an egg could have been released before the pill was taken," Schwarz says. So logic would follow that your friend's probability of getting pregnant increases the longer she waits. In fact, a World Health Organization study that says, "Delaying Plan B until the fifth day after unprotected intercourse increases the risk of pregnancy over five times compared with administration within 24 hours."

So yeah, if your friend waits five days, it's only about 25 percent effective. She's pretty much rolling the dice on that one.

What Will Probably Happen: Do the math. If your friend waits a few more days, to take Plan B, it will only 25 percent effective.

What You Should Tell Your Friend: "If it's been less than a week…and [your friend] would really like to avoid becoming pregnant, have a copper IUD placed ASAP," Schwarz advises. "IUDs are among the safest and most effective forms of contraception and are very good at preventing pregnancy even when placed up to seven days after unprotected intercourse." In fact, you can tell your friend that a nonhormonal copper IUD is more effective than the morning after pill, and it has the same level of effectiveness if inserted on day one or day seven. She'd also have a birth control method that would potentially last for 12 years. There's also Ella—a pill considered twice as effective as Plan B—that doesn't lose efficacy between day one and day five. Ella does, however, require a prescription.

If you don't want to say all of that, and your friend is still within the 72 hour window: Just find a place that sells Plan B, and offer to go with her to get it.

Read This Next: Why Aren't More Gynecologists Recommending IUDs?