What is the Pill?
The combination birth control pill, commonly known as the Pill, is an oral contraceptive that contains synthetic forms of two hormones, estrogen and progesterone. (Synthetic progesterone is known as progestin.)
With most brands, you take one pill every day for 21 days and then take nothing or a dummy pill that contains no hormones for the next seven. During this last week, your hormone levels drop off, causing you to get your period. When you've completed the 28-day cycle, you start a new pack of pills the very next day.
(Note: There's also a progestin-only birth control pill, known as the mini-pill. It's slightly less effective than the combination pill, but may be a good alternative for women who want to use an oral contraceptive but who are breastfeeding or can't take estrogen for some other reason.)
How does the Pill prevent pregnancy?
When the Pill is taken as directed, the estrogen and progestin work together to prevent pregnancy primarily by suppressing ovulation. This means they keep your ovaries from releasing any eggs.
The progestin in the Pill has other contraceptive effects, too. It thickens your cervical mucus, making it hard for sperm to get through your cervix and into your fallopian tubes to fertilize an egg, if one is released. The changes in your mucus may also make it harder for sperm to penetrate the tough outer coating of an egg. Finally, progestin thins the lining in your uterus, making it less likely that an egg would implant if it did get fertilized.
Can I use the Pill if I'm breastfeeding?
Maybe, but not right away. Whether or not you're breastfeeding, you'll want to wait 6 weeks after your baby arrives to start taking the Pill or any other estrogen-based contraception, such as the patch or the ring. That's because the risk of blood clots from these methods is highest right after birth.
After 6 weeks, if your breastfeeding is going well, it's okay for you to take the Pill. If you're not producing as much milk as you'd like, or if your baby is having any trouble nursing, though, the Pill may not be a good choice for you, because it may reduce the amount of milk you produce by a bit.
How effective is the Pill?
When taken correctly and consistently, the Pill is estimated to be about 97 percent effective in preventing pregnancy. This means that only three women out of 100 who take the Pill properly will get pregnant in the first year.
If you don't take the Pill exactly as prescribed — for example, if you start a new pack late or miss pills without using back-up contraception — the likelihood that you'll get pregnant is much higher. And the more mistakes you make, the higher the risk. (For the typical user, the Pill is about 92 percent effective, meaning 8 women out of 100 will get pregnant in the first year.)
So while the Pill is one of the most reliable methods of birth control available for women who follow instructions to the letter and never miss any pills, it's not the best method for everyone.
If you think you'll have trouble taking the Pill properly, consider using another method, such as the IUD, implant, patch, ring, or the birth control shot (Depo-Provera), all of which are very effective.
Although the Pill is an excellent contraceptive method, it doesn't offer any protection against sexually transmitted infections (STIs). So if you're at risk for STIs, you'll need to use condoms as well.
What will I need to do if I decide I want to get pregnant again?
All you have to do to reverse the effects of the Pill is to stop using it. You don't have to finish your pill pack unless you want to. Whether you finish your pills or not, you'll most likely get your period within a few days after you stop. For many women, fertility returns as soon as they stop taking the Pill, but some may take a month or so to start ovulating again.
Some practitioners recommend using a barrier method of contraception, such as condoms, and waiting until you have a couple of normal periods before trying to conceive because this can help you establish a more accurate due date. Others will give you the go-ahead to start trying right away if you want to. If you do get pregnant before your periods become regular again, don't worry — you can have an early sonogram to date your pregnancy.
(NOTE: You'll also need to start taking folic acid or a prenatal vitamin at least a month before you start trying to help prevent certain birth defects. That means beginning while you're still taking the mini-pill.)