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How soon you need to take Plan B emergency contraception — and other advice from an expert

As availability of Plan B emergency contraception has grown in recent years, so too have misconceptions about the drug. But with one in five never-married women using it at some point, according to the Centers for Disease Control and Prevention, it’s crucial that women know exactly what they are taking. Lisa Masterson, MD, a Los Angeles-based ob-gyn, has some answers.

“An emergency contraceptive is usually a hormonal type of pill. It’s very effective if taken within three days,” Masterson tells Yahoo Lifestyle. “A lot of them will say up to five days, but the further out that you take them from the unprotected intercourse event, the less effective they are going to be.” Based on the information from Plan B’s website, If the pill is taken within 24 hours of unprotected sex, it will be 95 percent effective; between 48 to 72 hours after unprotected sex, there’s a 61 percent chance that it will prevent pregnancy.

While the drug can be hugely beneficial, it’s not necessarily painless. “After taking the emergency contraceptive, you might expect breast tenderness, nausea, vomiting, headache — because it’s a high-dose birth control pill for most of them,” says Masterson. “And you might expect some irregular bleeding. That’s why sometimes it’s difficult to tell if you’re pregnant or not. So that’s why we still recommend taking a pregnancy test after that first initial bleeding to make sure it is in fact a period.”

Luckily, however, it’s easier than ever to procure. The drug is legally available over-the-counter in all states, and on its website, Plan B offers a store locator to make it easy to find out where it can be purchased. Masterson encourages women to find out ahead of time where they can purchase the medicine, so that they have it on hand if the need arises.

But whether or not you need it, she wants to make sure that misconceptions about the drug are dispelled. “A really common misconception about emergency contraceptives is that it’s an abortion, that it causes the release of the fetus or the embryo — and it does not,” says Masterson. “It is about stopping ovulation.”

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