Maybe you were rushing one morning and forgot to take it. Maybe you didn’t refill your Rx before a trip and missed a week. Or maybe you've decided now's the time to start trying for a baby.

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Regardless of the reason, almost every woman who takes birth control pills skips or stops at some point. But it’s a little scary: You’ve been faithfully swallowing that same little pill every day, at the same time, for years. What’s happening in your body when you miss one, two, or more?

First, some background: Birth control pills work to prevent pregnancy by preventing ovulation, says Alyssa Dweck, M.D., a gynecologist in New York and assistant clinical professor at Mount Sinai School of Medicine. Most pills contain synthetic forms of two female hormones—estrogen and progestin. (One type, called a mini-pill, has progestin only.)

These synthetic hormones stabilize your natural hormones and prevent the peak of estrogen that would otherwise signal your body to ovulate, or release eggs from the ovaries to be fertilized. But skipping one pill and skipping several are two very different matters.

What Really Happens When You Miss or Stop Taking Birth Control Pills If You Miss One Pill

Relax. “All of us have missed a pill or two—we’re only human!” says Sherry Ross, M.D., OB/GYN at Providence Saint John’s Health Center in Santa Monica, California. Take it as soon as you remember or take two pills the next day at the same time. “The chance of you getting pregnant is really unlikely if you get back on track quickly,” Ross says.

Two Pills

Double up on pills the next day and the following one. Still, the chance of pregnancy is very unlikely, so no need for a backup method, Ross says. (Though there’s a chance you’ll notice nausea or breakthrough bleeding, Dweck adds.)

Three or More Pills

Here's where it gets complicated. At this point, your hormone levels are disrupted, which lowers the pill’s effectiveness. If you had sex during that time, Dweck recommends taking emergency contraception (Plan B). Then throw out your old pack and start a new one—contact your healthcare provider if you need a new pack. “You must use a backup form of contraception, such as condoms, for one week,” Dweck says.

If You Decide to Stop Taking the Pill

There’s no waiting period to bring your body back to its baby-making ways. Once you stop taking the pill, the extra hormones leave your body, and you can start ovulating again—meaning you can pregnant right away, Dweck explains. (If your goal isn't having a kid, condoms or another form of contraception are a must!)

As for other effects? The way your body reacts really depends on why you started taking the pill in the first place, Dweck says. Women get on the pill for many beneficial reasons, such as more regular cycles, lighter periods, fewer cramps, improved symptoms of PMS (and the more severe version, PMDD), and clearer skin. The pill can also be used to treat polycystic ovary syndrome (PCOS). Treatment options for polycystic ovary syndrome. Badawy, A., and Elnashar, A. International Journal of Women's Health. 2011; 3: 25–35.

When you stop taking it, you’ll likely experience the same issues you dealt with before, Dweck says. This could mean irregular, heavy, or painful periods; cramps; acne; or other PMS symptoms (think headaches, cravings, and breast tenderness) return in full force. But as long as your periods were regular before the pill, your periods (and ovulation) will resume as soon you stop.

Note that some women experience what's called post-pill amenorrhea, Dweck says. Meaning you may not get a period for two to three months after stopping the pill as your body readjusts to normal hormone production. (If it's been three months, take a pregnancy test and see your doc.)

Also, you may also actually be able to feel yourself ovulating. About 20 percent of women may feel cramps or discomfort in their lower abdomen as their ovaries get ready to release an egg. Another sign of ovulation: an increased amount of cervical mucus (that fluid that looks like egg whites) on your underwear.

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However, for some women, Ross says the pill can cause unwanted side effects, such as bloating, feelings of depression, decreased sex drive, and headaches. “In some cases, women report upsides of going off the pill, including a better libido, weight loss, and more stable moods,” says Jennifer Wider, M.D., women’s health expert and author of The Doctor’s Complete College Girls’ Guide to Health. But this really varies from person to person. In other words, just because your friend says she feels fantastic off the pill, it doesn’t necessarily mean you should stop taking it.

Quitting the pill means you may miss out on other health benefits, including a decreased risk of ovarian, uterine cancer, and possibly colorectal cancer, though research is ongoing. The use of hormonal contraception and its protective role against endometrial and ovarian cancer. Grimbizis GF, Tarlatzis BC. Best practice & research. Clinical obstetrics & gynaecology, 2009, Oct.;24(1):1532-1932. Oral contraceptive use and risk of colorectal cancer. Fernandez E, La Vecchia C, Franceschi S. Epidemiology (Cambridge, Mass.), 1998, Jun.;9(3):1044-3983. And the longer you’re on it, the more protection you’re afforded, Dweck says.

The Takeaway

Missed one or two pills? Make them up ASAP. Three or more? All bets are off. Start a new pill pack and use a backup method for seven days.

But deciding to stop taking the pill altogether is an individual choice, and you should talk to your OB/GYN before going cold turkey. “Oral contraception has many health benefits—in addition to birth control,” Dweck says. As long as you’re not having issues, there is no reason to worry about being on the pill for extended periods of time. The bottom line: “For most women, the health benefits outweigh the risks or side effects,” Ross says.

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