How Long Does It Take For Birth Control Pills To Start Working?

Photographed by Ashley Armitage.
If you're cracking open your first pack of birth control pills, welcome to the club! Or perhaps you've been struggling to sort out which birth control method works best for you and are about to try yet another pill with a different blend of hormones. Either way, getting new birth control can be an exciting sort of experiment — at least, it's helpful to think of it that way.
There are plenty of good reasons why people go on birth control, but the biggie is, of course, to prevent pregnancy. So, how long does it take for the pill to kick in? It's a little complicated, and figuring it out starts with understanding exactly how pills do their thing in the first place.
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Hopefully your Ob/Gyn explained a little bit about the process before sending you off with a prescription, but just in case you weren't paying attention: Birth control pills give your body a pre-set amount of hormones that suppress ovulation. That means your ovaries won't release an egg. And with no egg to be fertilized, you won't get pregnant, says Taraneh Shirazian, MD, assistant professor in the Department of Obstetrics and Gynecology at NYU Langone Medical Center.
There are basically two kinds of hormonal birth control pills: a combination pill, which contains a blend of estrogen and progesterone, and a progesterone-only pill, which — you guessed it — only contains a synthetic version of progesterone. They work essentially the same way and will "override your body's natural surges, to create a cycle yourself," Dr. Shirazian says.
You're usually directed to start taking the combination pill on the first day of your period (or within five days of the first day of your period) because that will give it the most time to work before you would normally ovulate. When taken that way, it'll start preventing pregnancy basically immediately, says Medline Plus. But you can also take it at any point during your cycle if you're willing to give it seven days to start working. For those seven days, you'll also have to use a backup birth control method.
The progesterone-only pill is a little more straightforward: You can start taking it at any point during your cycle and expect it to kick in after 48 hours. But, again, you'll need to be using another form of birth control during those 48 hours to fully prevent pregnancy.
But just because your new pill is "working" doesn't necessarily mean "working for you" — as in, you feel good on it and any side effects aren't driving you nuts. When you're trying a new type of birth control, it's a good idea to give yourself a few months before you decide whether or not you want to stick with it. "I would say usually there's a three-to-six month minimum on any pill because your body needs to get used to that regular amount of hormone," Dr. Shirazian says. If you've been taking it for six months and you don't feel good on it, it's not regulating your cycle, or you're experiencing uncomfortable side effects, Dr. Shirazian recommends switching.
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However, these are just suggestions — it's crucial to check in with your doctor before you assume that your birth control has you completely covered, or before you decide to give up on it. Birth control is great, but it's not completely perfect at protecting against pregnancy, and the pill doesn't protect against STIs, Dr. Shirazian says. "Birth control [pills] need to be taken exactly correctly and at the same time to be 99.9% effective," she says. "In general, the problem that we have with the pill is human error." In other words, it's on you to remember to make the most of your birth control by taking your pill at the same time, every damn day.
If you're not trying to get pregnant and have just started a new birth control pill, you should probably use a backup method for at least a month just to be safe. Even if you've been on the pill for a while, you might want to consider using a barrier method in tandem — it's always better to be safe than sorry.
And remember, it can be confusing to start a new birth control method, even if it is just another type of pill. If this one doesn't turn out to be the perfect one for you, you and your doctor can work together to figure it out. "There are lots of methods out there," Dr. Shirazian says, "it's just about finding the method that's best for you."
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