In a way, birth control mimics the body's response to pregnancy. "There is some truth to the idea that birth control pills trick your body into thinking you're pregnant," said Dr. Vanessa Cullins, Planned Parenthood's vice president of external medical affairs. Here's what else you need to know if you're taking birth control.
  1. Birth control pills prevent pregnancy through two different mechanisms
    All birth control pills use hormones to prevent pregnancy. Some contain a hormone called progestin. Others contain two hormones, progestin and estrogen. All of them work by doing two things: They prevent women from ovulating, and they cause the cervical mucus to thicken, which makes it more difficult for a sperm to penetrate and make contact with an egg if the woman is ovulating.
  2. Lots of women take birth control incorrectly
    If women follow the exact instructions for taking birth control pills — every day, at the same time — they prevent pregnancy in 99 percent of all cases. But lots of people don't do that. In real life, birth control pills have a 9 percent failure rate. That means nine of every 100 women using birth control pills as their only means of contraception become pregnant in any given year.
  3. There's a three-hour window for taking your birth control pill "on time"
    A three-hour difference, for example, is not enough to lower the pill's efficacy. For combination progestin-estrogen pills, the space is even wider. Women who miss one day of their pill can take two pills the next day without reducing their birth control's effectiveness.
  4. Missing a period on the pill doesn't mean something's wrong
    Missing a period while on the pill doesn't indicate anything abnormal, Cullins said, as long as you have been taking the pill consistently and correctly each day. This is not permanent: When a woman stops taking birth control pills, the ovaries start making more estrogen, the uterine lining gets thicker, and women start to bleed again. Missed periods after taking your pills incorrectly, however, could indicate a pregnancy. In that situation, it's worth taking a pregnancy test.
  5. We don't know whether most antibiotics make birth control less effective
    There are two antibiotics that researchers have found make birth control pills less effective: griseofulvin, an antifungal used to treat athlete's foot and ringworm, and rifampicin, which is typically used to treat tuberculosis. Lots of antibiotics come with warnings that they'll make birth control ineffective. While a backup method is never a bad idea, there's actually sparse evidence that these other drugs make birth control less effective.
  6. Those "sugar pills" at the end of a birth control pack? They have active ingredients.
    Lots of birth control packs have four weeks of pills: three weeks of pills that prevent pregnancy and one week of pills that are inactive. Women can safely skip that last week of pills and still prevent pregnancy, Cullins said. But that doesn't mean the last week's pills are just sugar pills. As it turns out, some of them actually have active ingredients to make the pills work better or aid in women's health.
  7. Even under Obamacare, not everyone with insurance gets free birth control
    The number of women getting free birth control pills has quadrupled under Obamacare, recent research shows. Two-thirds of women in a recent Guttmacher Institute survey reported paying zero dollars for their contraceptive. The one-third of women still paying for their birth control are most likely in grandfathered health insurance plans.