Medically reviewed by Kristin Hall, FNP
Written by Our Editorial Team
Last updated 8/10/2022
Birth control pills are highly effective at preventing pregnancy. However, like other medications, it can take up to one week before the hormones in your birth control pills actively prevent you from becoming pregnant.
A variety of factors can affect how long it takes for birth control to start working, from the time of your period to the type of birth control pill you use. Below, we’ve explained how birth control pills work, as well as how long you’ll need to wait before you’re protected against pregnancy.
Currently, there are two different types of birth control pill available. The first, and most common, is combined birth control. Combined birth control pills contain estrogen and progestin hormones that work together to prevent you from becoming pregnant.
When you use combined birth control, your ovaries stop releasing eggs (prevention of ovulation). This lowers your risk of becoming pregnant by making it significantly more difficult for sperm to come into contact with a released egg.
Combined birth control pills also thicken your cervical mucus, making it more difficult for sperm to travel into your uterus. The lining of your uterus also changes, preventing sperm from coming into contact with an egg and causing pregnancy.
The end result? When used perfectly, the combined birth control pill is 99 percent effective in preventing pregnancy. However, under normal use, it’s about 91 percent effective.
The second type of birth control is progestin-only birth control, or the “mini-pill.” Mini-pills work slightly differently from combined birth control. Instead of containing a combination of estrogen and progestins, mini-pills only contain a single progestin hormone.
This hormone is included at a lower dose, meaning the total amount of hormones you receive from each pill is significantly lower than a combined birth control pill.
Progestin-only birth control pills stop pregnancy by thickening your cervical mucus, making it more difficult for sperm to come into contact with a released egg. They also thin the lining of the uterine cavity, making it difficult for a fertilized egg to implant there.
While progestin-only birth control pills may occasionally stop ovulation, they aren’t as consistent as combined birth control. Approximately 40 percent of women still ovulate while using the mini-pill, meaning your body might continue releasing eggs even while you’re taking the pill.
Our guide to combined birth control vs. progestin-only birth control goes into more detail on the differences between these two contraceptive options, as well as different things to consider when deciding which type of birth control is right for you.
Because each type of birth control pill works differently, the amount of time you’ll need to wait for full protection can vary depending on the type of pill you use.
If you start taking combined birth control within five days from the start of your period, it will begin working to protect you against pregnancy immediately.
Despite this, it’s still best to use condoms or another secondary form of birth control for at least one week after you start using the pill. This further lowers your pregnancy risk and protects you if you forget to take a pill or take a pill late.
If you start taking combined birth control more than five days after the start of your period, or at another time in your menstrual cycle, you should use a secondary form of birth control for seven days to avoid any chance of becoming pregnant.
After seven days, the combined birth control pill will provide maximum protection against pregnancy with “perfect use” - for instance, if you take it at the same time every day without ever missing a pill, you don’t vomit after taking it, and you aren’t taking certain medications or supplements that may interfere with its effectiveness. However, as we mentioned above, perfection is often hard to come by -- with “typical use” of the combined birth control pill, it is 91 percent effective at protecting against pregnancy.
Unlike the combined birth control pill, there’s no need to wait until the beginning of your period to start using the progestin-only mini-pill.
The progestin-only pill takes approximately 48 hours to start providing protection. You’ll need to use a secondary form of birth control for at least two days after you start using the progestin-only mini-pill.
After 48 hours, the mini-pill is 91 percent effective at preventing pregnancy with “typical use”. If taken perfectly, the pill is 99 percent effective at preventing pregnancy — but again, most of us aren’t perfect.
Because the mini-pill uses a lower dose of hormones, it’s extremely important that you take it at the same time every day. If you’re late taking your pill, or you miss your pill entirely, make sure you use a secondary form of birth control for at least the next 48 hours to keep yourself protected.
If you’re using birth control to treat and prevent acne, you’ll need to wait for two to three months before you’ll notice significant results. Our guide to birth control and acne goes into more detail about birth control and its potential as an acne treatment.
Used according to the instructions, birth control pills are highly effective at protecting you from becoming pregnant. They’re also thought to be generally safe for most women who take them, with millions of women in the United States and hundreds of millions worldwide using birth control pills.
Like with any medication, it’s important to allow birth control time to start working. If you’ve just started using birth control, follow your healthcare provider’s instructions to make sure you’re protected against pregnancy during the first few days of using your medication.
Would you like to learn more about birth control? Our guide to birth control side effects looks at how common birth control side effects are, while our guide to the different types of birth control covers all the options of birth control available, and how you can select the best form of it for you.