How do birth control pills work?
There are different types of birth control pills, but most types of hormonal birth control work by inhibiting your ovulation. If your ovaries don’t release an egg each month, you cannot get pregnant.
Birth control pills typically contain estrogen and progesterone. Some pills contain only progesterone. These hormones both work to change your natural menstrual cycle and stop ovulation, although 40 percent of people who use the minipill (progesterone-only birth control) continue to ovulate.
With most combined birth control prescriptions, you take active pills for 21 days and then placebo pills (or no pills) for seven days. These seven days are known as the “rest week.” Even though you’re not taking any hormones on these days, the pill is still working to prevent pregnancy. You usually get your monthly bleeding during these last seven days, but it’s withdrawal bleeding, not a real period. There are some oral contraceptives that have 24 active pills and four placebo pills. And for progesterone-only pills, you typically take them for 28 days straight and then immediately start the next pack.
Birth control also prevents pregnancy by thickening your cervical mucus, which makes it harder for sperm to reach your uterus. It also makes your endometrial lining thinner so it’s less likely to support a fertilized egg.
Does birth control stop periods?
Technically speaking, yes. The “period” that you get when you’re on birth control isn’t the same as a regular period. Without hormonal birth control, the lining of your uterus gets thicker to prepare for possible pregnancy and then sheds during your period if you’re not pregnant. Your body doesn’t ovulate or go through this regular menstrual cycle when you’re taking oral contraceptives. Instead, what you experience as a period on birth control is called withdrawal bleeding.
This bleeding occurs as a response to your body not receiving the same hormones during the rest week at the end of your 21-day pack. That means that if you continue taking the pill and skip the rest week, you can skip your “periods” too. Make sure to talk to your health care provider about whether this is a good option for you.
When do you get your period on birth control pills?
Once you’ve started your seven-day break from the pill each month, you’ll usually start to bleed two to four days into the pill-free week. This varies for each person, but birth control tends to make cycles very regular. That means that after a few months on the pill, you’ll probably find that your “period” usually starts on the same day of that week every month.
You’ll probably be getting your withdrawal bleeding every 28 days, but even after your body has gotten used to the pill, you can still experience late "periods" on birth control.
Keep in mind that your birth control only works effectively if you take it correctly. If you’ve forgotten to take three or more non-placebo pills, you could experience withdrawal bleeding before your seven-day break is scheduled. This would mean that you are no longer protected for the month and that you need to use a backup method of birth control and start a new pack.
Does missing a withdrawal bleed on a pill-free week mean I’m pregnant?
If you’ve been taking your pills according to the instructions, the pills will be 99.7 percent effective, even if you didn’t experience any withdrawal bleeding. The efficacy of the pill depends on you taking the pill at approximately the same time every day.
However, it’s important to remember that no birth control method is 100-percent effective. If you’ve missed a withdrawal bleed on birth control and want to be sure, you can always take a pregnancy test.
If you’ve missed three non-placebo pills or more, your chances of ovulating will increase. If you don’t experience any bleeding for a few days after missing the pills, take a pregnancy test. It’s also a good idea to take a pregnancy test if you miss two periods in a row while on birth control.
Possible reasons for missed withdrawal bleeding on birth control
Clinical Professor of Obstetrics and Gynecology Barbara Levy explains why people can sometimes experience no withdrawal bleeding on their pill break:
- When taking combined hormonal birth control, especially with the lower estrogen formulations, the lining of the uterus becomes very thin. For some people, the lining is thin enough that there isn't anything built up during the month to shed during the placebo week. And regular withdrawal bleeding does rely on enough lining growth to shed. As the doses of estrogen in the pills have gotten lower and lower over the years, there are more people who experience irregular or no withdrawal bleeding.
- In the case of the progesterone-only pill, the growth of the uterine lining requires estrogen “priming” — estrogen alone before progesterone is secreted after ovulation. And the role of progesterone is to maintain this growth. With progesterone-only pills, the progesterone is present throughout the month, which suppresses growth of the lining. Sometimes the lining becomes so thin (atrophic) that there isn't any tissue there to shed. And that’s why you can experience no withdrawal bleeding when you use this type of contraception.
Is it safe to skip periods with birth control?
Health care providers have been prescribing birth control to stop periods for a long time. Some people on birth control choose to skip their period only for special occasions (for example, maybe you expect your period to arrive during your wedding or a vacation and would like to avoid it). Other people use birth control to stop their periods if they have conditions such as endometriosis or period-related anemia.
Scientific research has found that using birth control to skip your period is as safe as taking your pills normally. If you’re interested in stopping your periods with birth control, though, it’s always a good idea to talk to your health care provider about it first.
No period after stopping birth control — what's that about?
If you’ve decided to stop taking the pill, it can take a while for your cycle to return to normal. This varies from person to person. Most people will have their period around two to four weeks after stopping the pill. However, your cycle may be irregular for some time. It’s normal for your body to need up to three months to go back to normal after stopping your birth control. If your cycles remain irregular for longer, make sure to visit your health care provider to find out the cause of your irregular cycles.
How to keep track of your menstrual cycle
You can use a menstrual tracker like Flo to keep track of your cycle. Period tracking apps let you log your symptoms and determine when you should expect your period. This can also take some weight off your mind, since you won’t have to remember when your period is due to arrive. The app will do it for you!
Overall, as long as you’re taking it correctly, birth control is highly effective at preventing pregnancy and those missed “periods” (withdrawal bleeding) can happen now and again.
If you’re not sure, take a pregnancy test to ease your mind. Adding some relaxing activities to your life and staying healthy can help get your cycle back to normal.