Welcome to Rumors I Heard About My Body, a recurring feature in which we answer questions about women's health in partnership with Planned Parenthood.
Q: I've heard that if you take Plan B more than three times, you can mess up your ability to get pregnant. Is this true?
A: Like lots of rumors about fertility — you can't get pregnant in a hot tub; Mountain Dew makes men sterile — this one about Plan B, which is a form of over-the-counter emergency contraception, is false. "No forms of emergency contraception affect women's fertility in the long run," says Dr. Raegan McDonald-Mosley, the chief medical officer of Planned Parenthood Federation of America.
Let's back up a second and explain how Plan B works. Plan B is just a super-powered version of a progestin-only birth-control pill (aka the mini pill). If you take it within five days of unprotected sex, it causes a delay in ovulation so the sperm can't fertilize the egg. If you want Plan B to be at its most effective, you should take it as soon as possible after unprotected sex. There is another morning-after pill, called Ella, that can be taken up to five days after unprotected sex, but like Plan B, it's most effective when taken as soon as possible.
There is some research showing that Plan B may not work as well for women who are overweight and may not work at all for women who are obese. Good thing there's a third option for emergencies for all women: a copper IUD. The copper IUD can be inserted (by a medical professional, of course) up to five days after unprotected sex and will work to prevent fertilization, and unlike either Plan B or Ella, once the IUD is inside you, it provides birth control for years, though you can have it removed if you decide you want to get pregnant.
Though the morning-after pill does not affect fertility levels, there are some side effects. Immediately after taking it, you may experience some nausea or vomiting. If you barf within two hours of taking it, you should get another dose, just to be sure you have digested the pill. Your next period might also be late, and you might spot (bleed a tiny bit) before that period. It's worth taking a pregnancy test a few weeks after you've taken Plan B just to be sure that it worked.
While the morning-after pill may prevent an unwanted baby, it won't prevent an unwanted case of the clap. If you've had unprotected sex with a new partner, you might want to get an STI screen. Also, don't have sex again without birth control. Morning-after pills don't provide prolonged protection the way taking a pill regularly does. Finally, if you're breast-feeding, you may need to pump and dump for 48 hours after taking the pill, because the burst of hormones will show up in your breast milk.
Have other questions about your body you want answered?
Email firstname.lastname@example.org. Jessica Grose is the editor in chief of Lenny.