You have probably heard the popular maxim that “the pill tricks your body into thinking it’s already pregnant,” as the reason for how it prevents pregnancy. But there’s also another way to look at it, which The Fifth Vital Sign author and Fertility Friday podcast host Lisa Hendrickson-Jack mentioned in her video interview with Natural Womanhood: that hormonal contraception tricks the body into thinking it’s in menopause. So which is it? Well, it’s tricky—it’s both (and neither).
Here’s how birth control works
Let’s review the mechanisms of how hormonal contraception works. All hormonal contraception attempts to prevent ovulation by delivering the body a steady spike of synthetic hormones. For the pill, this is delivered every 24 hours you take it. For the vaginal ring, it’s constantly delivered over the 21 day cycle of wearing it. For the (hormonal) IUD, it’s a constant stream of hormones being released from the device for the years while wearing it.
Hormonal contraception contains one or a combination of two forms of synthetic hormones that mimic either progesterone or estrogen. Progestin, the artificial form of progesterone, is essential to the mechanism of preventing ovulation. Therefore, all hormonal contraception contains a form of progestin. Some hormonal contraception also contains an artificial form of estrogen, such as Ethinylestradiol or Estradiol valerate (E2V). The main reason hormonal contraception contains synthetic estrogen is to mimic a real period. The bleeding you experience on these “combined” forms of hormonal contraception is a result of the withdrawal of synthetic estrogen during the week you take the “sugar pills” (i.e., the non-hormone containing pills) in your pack.
If you take the “mini pill” or any other hormonal contraception that contains only progestin (and no synthetic estrogen), you may notice either an absence of bleeds all together, or sporadic, light, and/or irregular bleeding or spotting. This is due to the lack of estrogen in these forms of contraception. Think of it this way: Estrogen is “the grower” and progesterone is “the glue.” Estrogen grows endometrial tissue, while progesterone holds it all together. A small amount of endometrial shedding occurs as a cellular response when there is a lack of both, to keep the endometrium from becoming too thickened and overgrown in the absence of a regular period.
How progestin (and pregnancy) stop ovulation from happening
Whether your pills contain estrogen or not, progestin does the bulk of the work in preventing pregnancy. Like real progesterone, progestin sends a negative feedback loop to the pituitary gland telling it “Stop! Wait! Don’t release an egg! We’re busy working on something down here!” Progestin—like real progesterone—also thickens cervical fluid in the cervix making it an inhospitable environment for sperm. This negative feedback loop happens naturally after ovulation in a cycle unaltered by hormonal contraception. In a natural cycle, the “busy working on something” is preparation for possible conception. The body doesn’t want to release an egg when there’s a chance one has already been fertilized.
However, unlike real progesterone, progestin doesn’t act on the uterine lining or other parts of the body the same way, and women can’t reap the benefits of real progesterone like mood stabilization, improved bone and heart health, and better sleep. In short, women on hormonal contraception are getting steady, low doses of either progestin or some combination of progestin and synthetic estrogen, both of which suppress the communication between the hypothalamic-pituitary-ovarian (HPO) axis, which would normally be responsible for triggering the monthly release of an egg from one of the ovaries (ovulation).
So… does birth control trick your body into a “fake pregnancy” or “fake menopause?”
In pregnancy, levels of estrogen and progesterone both soar to extremely high heights, steadily increasing throughout the entire pregnancy. (More than 500%!) Progesterone, as well as Human chorionic gonadotropin (HCG—the hormone a pregnancy urine test looks for) send the signal across the HPO axis to halt starting a new period or releasing a new egg.
Comparatively, in menopause, estrogen and progesterone levels are so low that it’s not really a suppression of the HPO axis as much as it is a natural deactivation. Estrogen is so low that ovulation doesn’t happen, and if there’s no ovulation, there’s no need for progesterone. Post-menopausal women continue to receive minimal amounts of estrogen from their fat cells, but receive virtually no progesterone. (A reason why healthy exposure to endogenous hormones throughout reproductive life is essential to post-menopausal health.)
A woman on hormonal contraception is similar to a post-menopausal woman since they both have low levels of the sex hormones estrogen and progesterone. (The doses of synthetic hormones in hormonal contraception are quite low compared to the levels seen in a naturally cycling or pregnant woman.) However, a post-menopausal woman doesn’t have anything suppressing ovulation, it’s just not happening naturally, which results in low hormone levels.
When no one is ovulating
The bottom line is that a pregnant woman, a post-menopausal woman, and a woman on hormonal contraception all have one thing in common: None of them are ovulating (save for the occasional breakthrough ovulation that can occur on hormonal contraception). Therefore the most accurate comparison for how birth control works, is that hormonal birth control tricks the body into thinking ovulation has already happened.
So it’s easy to say that hormonal birth control tricks the body into thinking it’s pregnant—and it’s sort of, kind of, true. It’s far less sexy to say that hormonal contraception mimics menopause, which is also sort of, kind of, true. But in reality, the pill tricks your body into….well, not ovulating. It does this by providing constant, daily (but low) spikes of synthetic hormones—which doesn’t really ever happen in any natural reproductive season.
With fertility awareness, you still get to ovulate—and reap the benefits of ovulation
If you think ovulation is simply an accessory—especially if you’re not actively trying to conceive— think again. In fact, we have an entire series about why ovulation is imperative for women’s health. While it may work to effectively prevent pregnancy, artificial suppression of the HPO axis can have damaging effects on a woman’s health. Luckily, with Fertility Awareness Methods (FAMs), a woman can ovulate, prevent pregnancy, and reap important health benefits without putting her body into an altered state. In short, there’s no reason to trick your body—period!
Additional Reading:
Shocking Reasons why Birth Control Lowers Women’s Sex Drives
Hormonal Birth Control Depletes Your Body of Key Nutrients
Can birth control cause infertility? Yes… and no
