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How Hormonal Contraception Works
Here’s what you need to know about hormonal birth control
Aug 16, 2023
Aug 16, 2023
Your HealthMarijke Vroomen Durning, R.N., is a freelance writer in Montreal, Canada. Her work has been published in many outlets over the years, both online and in print. Marijke often describes her writing as the bedside teaching nurses want to do but rarely have the time for. Her experience working in healthcare has taught her what types of information people need and how to share it. One such need is medication and drug safety, so Marijke wrote the book," Just the Right Dose: Your Smart Guide to Prescription Drugs and How to Take Them Safely."
Marijke is a member of the Association of Health Care Journalists (AHCJ), the American Society of Journalists and Authors (ASJA), and the Authors Guild. She is also a member of the Canadian Nurses Association (CNA) and is registered with the Ordre des infirmiers et infirmières du Québec (Order of Nurses of Quebec).
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Here’s what you need to know about hormonal birth control
Medically reviewed by Barbara Dehn, R.N., M.S., N.P.
People have more than 50 hormones circulating in their blood. These chemicals carry messages throughout the body to control metabolism (the process of changing food into energy), growth and development,sexual function, and many other things.
Estrogen and progesterone help women become and stay pregnant. Estrogen helps release eggs (ova) from the ovary. Progesterone prepares the uterine lining to support a pregnancy after an egg is fertilized by sperm.
Hormonal birth control using estrogen and progestin (a form of progesterone) stops the ovaries from releasing eggs and changes the uterine lining so it won’t support a fertilized egg. The hormones in birth control also prevent pregnancy by changing the quality of the mucus at the cervix, which blocks sperm from moving up into the uterus.
The most commonly used birth control pills are called combination pills, which contain both estrogen and progestin. But there are estrogen-free pills available for people who can’t — or prefer not to — take estrogen. Some reasons you may want to avoid estrogen include:
Estrogen-free pills work really well. They have a slightly lower effectiveness rate than combination pills, but they are still very effective — up to 99% if taken “perfectly.” However, since people aren’t perfect, and it’s easy to forget or miss pills, this type of pill is about 91% effective in reality.
There is not a lot of information on the efficacy of birth control pills in women with overweight or obesity because women with higher BMIs were often not included in clinical trials. There is one estrogen-free pill (Slynd), however, that included women of higher BMIs in their clinical trials and found it to be effective in a wide range of body types.
Pregnancy protection starts right away if you take combination pills within five days of starting your period. For estrogen-free pills, pregnancy protection begins one to two days after you start taking them, depending on which pill you take and where you are in your cycle.
It's important to take birth control pills every day. For the combination pill, you can take it any time of the day, as long as you take it every day. For the estrogen-free pill, you need to take it at the exact same time every day.
For most estrogen-free pills, there’s a three-hour window to take a missed pill. But there is one newer estrogen-free option that allows you a 24-hour window if you’ve missed a pill. Talk to your pharmacist about your drug’s timing and read the instructions with your prescription.
No matter which type of hormonal contraceptive you use, it’s important to use a backup method such as condoms until the pills are effective. Also note that hormonal contraceptives do not protect against sexually transmitted infections (STIs).
Most women who stop taking hormone contraceptives can become pregnant shortly after they stop using them (pills or vaginal rings) or have them removed (implant). It can take a few weeks to a few months, because the estrogen in these contraceptives stops ovulation. On the other hand, estrogen-free pills only affect the uterine lining, so once you stop taking them, the lining returns to its usual state and can support a pregnancy. This can happen in a few days or a few weeks.
With combination birth control pills, you usually get your period every month at the same time. The combination hormone pills come in a package with 28 pills, but only 21 have hormones. The others are placebos (so-called sugar pills) for you to take so you don’t get out of the habit of taking it or forget when you last took it. This is also when you would have your period.
Estrogen-free contraceptives don’t usually have placebos. But, there’s one estrogen-free brand that has 24 hormone tablets and four placebos. With all hormonal contraception, you may experience breakthrough bleeding, especially when you first start taking the pills.
Some women stop having periods while taking estrogen-free birth control pills, while others may have a period around the last week of the packet. Hormonal birth control pills can be helpful for women who have irregular or heavy monthly periods.
If you’re using one form of contraception and want to switch to another, ask your healthcare provider about your options, and when the best time is to make the switch.
This resource was created with funding support from Exeltis, USA.