Will Taking Plan B Cause a Miscarriage?

The Short Answer Is No. What's More, the Drug Has Some Advantages

woman with pill and water in hand
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Plan B One-Step (levonorgestrel) is a type of emergency contraception that's sold over-the-counter to be purchased and used to prevent pregnancy by a woman who has had unprotected sex. A common misunderstanding about Plan B is that it causes a miscarriage. However, the drug, which also is available under the brand names Fallback Solo, Next Choice One Dose, and Opcicon, prevents conception from happening in the first place. By the time a pregnancy can be confirmed with a positive result on a home pregnancy test, an embryo will have already implanted in the walls of the uterus and taking Plan B will have no effect on it.

Although contraceptives such as Plan B should be regarded as a backup form of birth control and never relied upon as a regular way to prevent pregnancy, they are a safe and effective way to deal with a potential emergency if used correctly after inadvertently unprotected sex. Here's how morning-after pills work, how they should be taken, potential side-effects, and other important information to know.

How Plan B Works

The active ingredient in Plan B and other morning-after pills is levonorgestrel—a progestin (a type of hormone) that is prescribed not only to prevent pregnancy but also for other reasons, including to treat endometriosis (a condition in which the tissue lining the uterus grows outside of the uterus), certain cancers, and appetite loss and severe weight loss caused by acquired immunodeficiency syndrome (AIDS) or cancer. In high doses, progestin may be prescribed as part of treatment for infertility in a woman whose body doesn't produce enough progesterone.

As emergency contraception, progestins work in three ways—by preventing the release of an egg from an ovary; by preventing an egg that is released from being fertilized; and by preventing implantation of a fertilized egg in the lining of the uterus. Which of these functions the drug performs will depend on where you are in your menstrual cycle. For example, if you've already ovulated levonorgestrel obviously can't stop that from happening, but it can prevent fertilization if the egg you released comes in contact with sperm.

Here are some situations in which you might be advised to use the morning after-after pill:

  • You and your partner had sex with using any birth control.
  • You used a condom but it slipped off or broke.
  • You were wearing a diaphragm that slipped out of place.
  • You missed taking at least two or three active birth control pills in a row.
  • You forgot to insert your ring or apply your patch.
  • Your partner didn't pull out in time.
  • You were forced to have sexual intercourse.

Be aware that Plan B and other morning-after pills will not protect you from sexually transmitted infections. The only ways to prevent STIs is by always using a condom (even during oral or anal sex) or by not having sex at all.

Taking the Morning-After Pill

Some brands of levonorgestrel, including Plan B, are taken as one pill; others are taken as two. In order for the drug to be effective, you must take the single pill as soon as possible within 72 hours (three days) of having unprotected sex. If you're taking it in two doses, swallow the first pill within 72 hours and take the second one 12 hours later.

Planned Parenthood says that you can take emergency contraceptive pills as late as five days after having unprotected sex. Just know that the sooner you use it the more likely it is to be effective. Also note that you should not take a double dose of levonorgestrel or two different brands of emergency contraception: Doing so will not increase the effectiveness of the drug and may even make your sick.

One of the possible minor side effects of taking levonorgestrel is nausea and vomiting. If you vomit within two hours of taking the pill, call your doctor. It's possible that you will need to take a second dose.

Other side effects associated with taking emergency contraception include:

  • Diarrhea
  • Fatigue
  • Headache
  • Dizziness
  • Breast pain or tenderness

Although taking the pill will not cause a miscarriage (because it will prevent pregnancy from occurring in the first place), you also may notice that when you have your next period it's heavier than usual. It's just as likely, however, that your flow could be lighter. Some women have experienced spotting or bleeding between periods after using emergency contraception.

Your period may come a week earlier or later than usual after taking levonorgestrel. If you don't get your period within three weeks, do a home pregnancy test or have your doctor test you to make sure the pill worked to prevent conception.

The only serious side effect that's been reported is severe abdominal pain three to five weeks after taking levonorgestrel. If this happens to you, see your doctor.

Is Plan B Right For You?

There are some women who should not take Plan B or other morning-after pills. It's not recommended for those weighing more than 175 pounds and may be less effective in women who weigh more than 165 pounds, for example.

The drug also may not be as effective for women who take certain medications. These include anticonvulsant drugs, antibiotics, the tuberculosis treatment rifampicin, the antimicrobial drug Mycobutin (rifabutin), Grifulvin V (griseofulvin) for treating certain skin infections, and St. John’s wort, a dietary supplement sometimes used to treat depression.

Women who have abnormal vaginal bleeding or may be allergic to any of the pill's ingredients also shouldn't take Plan B. And if know you're already pregnant, you should not take Plan B. However, don't worry if you take the drug and then discover that you're expecting: According to Planned Parenthood, it won't harm your pregnancy.

If you're considering using emergency contraception, note that there are more effective options than Plan B and similar morning-after pills. These include having a ParaGard IUD inserted within five days or getting a prescription for Ella (ulipristal acetate), which also must be taken within five days after having unprotected sex but is as effective at that point as it is on day one.

Advantages of Morning-After Contraception

One advantage of morning-after pills containing levonorgestrel is that they are available over-the-counter in the family planning aisle of pharmacies, supermarkets, and chain stores, can be purchased by anyone of any age or gender (so you do not have to show an ID to buy a morning-after pill), and are relatively affordable. According to the American Society for Emergency Contraception, in July 2013, the average price of Plan B One-Step was $48, while generic versions cost $41 on average.

Prices were generally lower at independent pharmacies than at chain stores, but the least expensive version of levonorgestrel is a product called AfterPill, which is available only online at afterpill.com for $20 plus $5 for shipping. AfterPill is good for 18 months, so it can be purchased ahead of time and stored in the event of an emergency.

As already mentioned, morning-after pills should be not be used a regular contraception, but it can be useful to know about and even have on hand. If you're sexually active and not sure what type of birth control is right for you, see your doctor or visit a local Planned Parenthood or women's health clinic for guidance. There are lots and lots of options, and so you should be able to find one that will give you the protection you need while also fitting in with your lifestyle.

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