Your Hormones and Hormonal Birth Control: What You Should Know
Melissa M. Keenan
How exactly do hormones and birth control overlap? We break it down in this straightforward guide.
The pill, the patch, the ring, the shot, the morning after pill, the IUD — there are so many forms of birth control available, each with their own advantages and potential drawbacks.
While it can seem overwhelming to choose the birth control that is right for you, many forms of birth control work in similar ways — by providing synthetic reproductive hormones. To manage your health, it’s important to understand how birth control works and how it interacts with natural hormones in the reproductive system.
How Hormones Work
Hormones are chemical messengers—they are created and released by endocrine organs and act elsewhere in the body on other organs or tissues. The major endocrine glands include the pituitary gland, thyroid, adrenal glands, pancreas, ovaries, and testes.
Most hormones travel in the body through the bloodstream or in the fluid that surrounds cells. Each hormone primarily impacts the cells that have receptors specific for that hormone. There are around 50 hormones in the human body¹, each with their own roles in physiological functions. Hormones control everything from growth and development to mood.
Reproductive hormones are those involved in fertility and sexuality². Reproductive organs produce varying levels of the reproductive hormones depending on a person’s age, reproductive status and general health. Some of the major reproductive hormones are gonadotropin releasing hormone, follicle-stimulating hormone, luteinizing hormone, estrogen, progesterone and testosterone.
Hormones and the Menstrual Cycle
Reproductive hormones influence the menstrual cycle³. When someone with ovaries reaches puberty, gonadotropin releasing hormone triggers the pituitary gland to produce two hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH)⁴.
FSH and LH are responsible for the development and maturation of follicles (fluid-filled ‘sacs’ that contain eggs), and ovulation (the release of a mature egg from the follicle)⁵. In response to increasing levels of estrogen from the ovaries, a surge in LH triggers ovulation. Once an egg is released from the ovary, the empty follicle continues to produce estrogen, and now also produces progesterone, which are needed to prepare the uterus for possible pregnancy⁵.
If the released egg does not become fertilized and implant in the uterus, the lining of the uterus is shed in a withdrawal bleed or period. This sequence of events occurs roughly every month and is called the menstrual cycle. Hormones drive physiological changes during different phases of the menstrual cycle³:
Phase 1: The Menses Phase
The menses phase is when your body sheds the extra endometrial lining it had prepared for a possibly fertilized egg. In other words, it is when you have your period. At the beginning of the menses phase, estrogen and progesterone levels are low. These hormone levels dropped at the end of the previous cycle. This drop is what causes your period or withdrawal bleed, which typically lasts 3-7 days.
Phase 2: The Follicular Phase
As a new cycle begins, the low levels of estrogen and progesterone cause increased production of FSH and LH from the pituitary gland. As these pituitary hormones rise, they stimulate the ovaries to increase hormone production. The primary hormone produced by the ovaries during the follicular phase is an estrogen called estradiol, and a smaller amount of progesterone is also produced. These hormone changes result in the recruitment of ovarian follicles that begin to mature³.
Phase 3: The Ovulation Phase
At the end of the follicular phase, the rising levels of estradiol and progesterone trigger a surge of LH production by the pituitary gland. This rapid rise in LH causes ovulation, the release of a mature egg from a follicle-- only one follicle matures completely and releases an egg. The released egg moves from the ovary to the fallopian tube and towards the uterus.
Phase 4: The Luteal Phase
The luteal phase occurs after the egg has been released from the follicle. Changes occur that would prepare a uterus for a pregnancy if the released egg becomes fertilized. The empty follicle continues to produce both estradiol and progesterone, but the now high levels of progesterone primarily drive the physiological changes in the luteal phase.
These rising hormone levels thicken the uterine lining in preparation for possible pregnancy. The thickening of the uterine lining is necessary for a fertilized egg to implant. If an egg isn’t fertilized and implanted in the uterus, the empty follicle stops producing estradiol and progesterone. As these hormone levels decrease, the menses phase is triggered, and the cycle starts all over again³ ⁵.
A quick caveat: The hormone changes discussed here are what is "typical" for someone with ovaries prior to menopause. However, due to medical conditions like PCOS or endometriosis, high or low body weight, stress, perimenopause, and a number of other factors, menstrual cycle patterns can vary quite a bit across individuals and over time.
Hormonal and Non-hormonal Birth Controls
The name birth control (aka contraception) is fairly self-explanatory — it works to prevent pregnancy before it happens. There are many methods of birth control. Today we are going to focus on hormonal methods and how hormones and birth control interact. But first, here is a quick overview of the various kinds of hormonal and non-hormonal birth control options.
Non-hormonal birth control
Non-hormonal methods contain no hormones and are available to those who prefer not to use hormones because of personal preference or medical necessity. They include:
There is currently one type of non-hormonal IUD available in the US. This IUD prevents pregnancy with copper, a super-effective spermicide that interferes with sperm transport, egg fertilization and possibly prevents egg implantation⁷, all without harming the person with the IUD.
Hormonal birth control
Hormonal methods contain an estrogen and a progestin or only a progestin. They include:
Combined contraception pill
All other IUDs
The morning-after pill (emergency contraception)
Just like non-hormonal methods, hormonal birth controls also have varying degrees of efficacy⁶.
How Do Hormonal Birth Controls Work?
While each hormonal birth control method has a slightly different mechanism of action, there are a few key, common mechanisms that work to prevent pregnancy. Some of these mechanisms are⁸:
Thickening cervical mucus
Changing the uterine lining
Many types of hormonal birth control prevent ovulation from occurring. Therefore, they stop a potential pregnancy early on in the process-- if no egg is released from the ovary, no egg can be fertilized!
Options for combined birth control pills
While the ways they work are generally similar, birth control pills are not all the same. They come in different formulations, with different doses and specific synthetic hormones.
Of the birth control pills that contain both an estrogen and a progestin (combined oral contraceptives), there are monophasic, biphasic, and triphasic pills8. Estrogen and progestin-containing birth control pills work primarily by preventing ovulation, but they also can impact the uterine lining and cervical mucus to prevent implantation and fertilization⁹.
Monophasic pills have the same amount of hormones in every pill, save for the placebo week, when the pill contains no hormones. You are still protected from pregnancy during this time, as the pill has prevented ovulation, so there is no egg to be fertilized⁸.
Biphasic and triphasic pills have different doses of the estrogen and progestin that mimic the hormone changes that occur during the menstrual cycle⁸.
Other hormonal birth control options
The mini pill - A less commonly used birth control pill called the "mini pill" contains only a progestin. It primarily works by thinning the lining of the uterus and thickening the cervical mucus. In some people, it can also prevent ovulation¹⁰. For this pill, there is no placebo week, which often results in periods stopping over time.
The patch and the ring - Both of these work in a similar way and contain an estrogen and a progestin. Both release hormones for three weeks and are removed for one week to trigger a withdrawal bleed. Whereas the ring is inserted into the vagina and hormones are absorbed vaginally, the patch is put on the upper body (the arm, abdomen, or buttock) and hormones are absorbed through the skin⁸.
The shot, hormonal IUDs, and the implant (Nexplanon) - These longer-acting methods of birth control contain only a progestin6. The progestin in the implant or IUD is released continuously over the period of a few years. The shot (Depo-Provera) is administered every three months. These progestin-only methods work by thinning the uterine lining and making cervical mucus thicker, preventing implantation and fertilization, and, in some people, also inhibiting ovulation⁸.
Emergency contraception - Plan B emergency contraception also is a progestin-only contraceptive. Levonorgestrel, the progestin found in Plan B emergency contraception, is the same progestin found in hormonal IUDs and many formulations of combined birth control pills¹¹. Emergency contraception can work at any point during the menstrual cycle because it helps prevent 1) the release of an egg from the ovary, 2) a released egg from being fertilized, and 3) a fertilized egg from attaching to the uterine lining. Plan B emergency contraception works best the sooner it is taken to when unprotected sex occurred.
Your Hormones on Birth Control
Understanding how hormones and birth control interact is important for understanding our bodies and our health. Now that you understand your hormones during your menstrual cycle and how they work in hormonal birth controls, you are ready to make your own precise choice, and adyn is here to help.
At adyn, we work with you to ensure that you find the best possible birth control for your individual physiology—whether your goal is preventing pregnancy, treating acne, or managing another health condition.
Reed BG, Carr BR. The Normal Menstrual Cycle and the Control of Ovulation. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext. South Dartmouth (MA): MDText.com, Inc. https://www.ncbi.nlm.nih.gov/books/NBK279054/ [Updated 2018 Aug 5]. Accessed 04/2021 to 10/2021.