Disclaimer: I'm not.a doctor. What I publish here are insights informed by my research and I cite sources at the bottom of each article. For diagnostic questions, contact your care providers.
I've been thinking for a while about how to continue explaining the science behind hormonal birth control (HBC) in a way that's interesting and accessible. All the while, I've been answering questions about HBCs and have come across several re-occurring and pretty massive misconceptions among users. So, I thought I'd unpack those questions for you here! Let's go one by one through some super-common myths and truths about HBCs:
Your Question: "I have PCOS/ HA. Will my periods become more regular on birth control?"
The top-level science: It's perhaps the single most perpetuated myth that hormonal birth control magically regulates your natural period. Rather, the 28-day manifestation of a bleed on HBC is pure branding on the part of drug makers. In reality, HBC simply gives you a synthetic withdrawal bleed.
Tell me more: As a reminder, HBC works by maintaining synthetic progesterone (and sometimes estrogen) in your system to mimic the second half of your menstrual cycle – your luteal phase. Essentially, these synthetic hormones trick your body into thinking you've already ovulated, so there's no need to release "another" mature egg. When you get to the end of your pill pack, take out your vaginal ring, or remove your patch, etc., you're triggering the same progesterone withdrawal that would occur naturally in your body if your corpus luteum had disintegrated naturally (except, reminder, without ovulation, there's no corpus luteum). Still, it's not fair to call this progesterone withdrawal bleed a period; your body has not gone through the menstrual cycle and you did not ovulate.
Why this matters: A majority of period abnormalities happen due to hormonal imbalances in the first half of a person's cycle, with delayed ovulation being the primary factor in cycle irregularity. When doctors put people with irregular cycles on HBCs, they're masking any underlying hormonal balance issues - not solving them.
As an example, someone with hypothalamic amenorrhea (HA) exhibits constant low FSH and LH levels, which keep their follicles from maturing and releasing; without mature follicles you'll experience anovulation and skip periods entirely. This underlying hormonal imbalance in the follicular phase is simply not fixable with a synthetic dose of progesterone or estrogen mimicking the luteal phase. And indeed, masking the critical indicator of this underlying health problem is unwise - I've noted before that HA has serious long-term health consequences.
Your Question: "Why is my period lighter/heavier/shorter/longer on birth control than it was before?"
The top-level science: Any change in the duration or nature of natural cycles has to do with your hormone levels, each of which can get "out of whack" for different reasons related to age, nutrition, stress and more. For people taking HBCs, I've already covered the fact that your "period" is really just a withdrawal bleed. Fluctuations in the nature and duration of withdrawal bleeds are common, with periods becoming lighter and shorter the longer someone spends on an HBC.
Tell Me More:
For pill-taking people, withdrawal bleeds become lighter and shorter due to one of the very reasons that HBCs are so effective at preventing pregnancy in the first place - the synthetic HBC hormones keep your uterine lining ultra-thin, so that it cannot sustain the implantation of a fertilized egg*. Not surprisingly, it may take a few cycles on HBCs to really thin-out the lining and reduce withdrawal bleeds.
As for natural menstrual cycles changing with age, the science in adolescence has to do with the Hypothalamus-Pituitary-Adrenal finding its "rhythm" to activate enough FSH and LH to trigger regular cycles.*
During the approximate decade before menopause, cycles de-regulate due to declining egg quality. Less "robust" eggs may not release as much estrogen, so will cause the pituitary to produce more FSH and trigger ovulation earlier in the cycle - resulting in a shorter cycle all together.*
It should be noted that there are also disorders that can cause cycle changes; Polycystic Ovarian Syndrome (PCOS) and Hypothalamic Amenorrhea (HA) are two extremely common hormone-based cycle disruptors that present quite differently. Other potential period problems include endometriosis, post-pill amenorrhea, fibroids, polyps, and more.
Your Question: "Doesn't HBC work by mimicking pregnancy?"
The top-level science: Woof - this one is so pervasive that if you do a quick Google search on "Hormonal birth control mimics..." the auto-fill will quickly populate your search with the myth answer to this question! The key mechanism HBCs use to eliminate your chance of pregnancy is the ingestion of synthetic hormones into your body, which actually suppress the natural estrogen and testosterone you make to levels akin to those of someone in menopause.
Tell Me More: What's true is that the synthetic progesterone and (in some cases) estrogen of HBC mimics the second phase of the menstrual cycle to convince your body it's already ovulated. It's also true that the beginnings of pregnancy are marked by increased progesterone levels, which continue to elevate past luteal cycle levels to ensure that the uterus is essentially nice and cozy for a developing zygote. HOWEVER - and this is a big however - HBCs is (say it with me) are synthetic versions of estrogen and progesterone and they actually dramatically suppress your natural estrogen and testosterone levels to the effect that the natural hormone profile of someone taking HBC will look more like that of someone in menopause. As one renowned OB-GYN described the impact of this reduction in natural hormone production in otherwise healthy women, "The havoc occurs slowly, but inexorably...Studies show birth control pills reduce the development of strong bones, negatively impact gut and immune health, damage vaginal and bladder health, and impact brains." (Source)
I hope this post has helped clear up some of the pervasive misinformation out there about HBCs and the menstrual cycle. Go forth empowered to make an informed decision regarding your own HBC usage!
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