How Does Birth Control Actually Work?

When it comes to birth control, condoms and other barrier methods are pretty easy to understand: they physically block sperm from joining up with an egg, like a World Cup-winning goalie. But the way the birth control pill works might be a little tougher to grasp, since all the work happens internally and out of sight. 

Time for a little learning. Here’s how birth control pills actually work, and how to take them correctly for maximum effectiveness.

What is the birth control pill?

The birth control pill is a daily oral contraceptive that contains pregnancy-preventing hormones. When used correctly, the pill can be up to 99% effective—but correct usage means taking it at the same time every day, which is where a lot of people slip up (so experts recommend pairing it with a daily activity, like brushing your teeth at night). 

How does the birth control pill work?

Quick review of the birds and the bees: you become pregnant when an egg released from the ovary is fertilized by sperm. That egg attaches to the inside of your uterus, where it develops into a baby. Your body’s hormones are in control of how the egg is released from the ovary (which is called ovulation), and those hormones also prep your body to accept the fertilized egg. 

So, with that scientific info in mind, birth control pills are a type of hormonal contraceptive, along with patches and vaginal rings. Most forms of hormonal contraceptives are filled with a tiny bit of human-made estrogen and progestin, and those hormones block your body’s natural hormones to prevent pregnancy in three different ways. 

First, they stop that ovulation we talked about earlier, so your eggs are never released from your ovaries. They also thicken your cervical mucus to make it harder for sperm to swim through the cervix and find an egg to fertilize. Finally, these hormones thin out the lining of your uterus to make it more difficult for an egg to attach once it’s fertilized. It’s a contraceptive triple threat.

How do you take birth control pills correctly?

We touched on this earlier, but it’s crucial to take birth control every day AND at around the same time of day for it to be as effective as possible. Most people make the pill a part of their daily morning or evening routines, so it becomes just another automatic step you take after washing your face or taking any other medications. And if you’re on a progestin-only mini-pill, you really need to take it within the same three-hour window every day—so set that aforementioned phone alarm and keep your pill pack where you can easily access it. (Here’s a quick refresher on what to know about progestin-only pills, FYI).