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Today we are going to kick off the Kick Ass Birth Control series by talking about America’s most popular method: the pill.

The thing is, the pill is so complicated and comes in so many different forms, it’ll have to be broken down.

This post focuses on how the pill works, and what this might mean for health and fertility.  The next installment will cover all the various types of pills, explaining and weighing pros and cons of each.

In addition to the posts in this series, you can find more information on birth control in the book I wrote, available here.

And briefly, beforehand, the world’s quickest announcement: the T shirt contest has been closed!  We got dozens of awesome designs.  Beautiful, fierce, simple, explicit, exquisite… so thank you, thank you so much, all of you, for caring about and loving this community. So I am sitting on some ideas and going through sketches with my artistic pals.  The T shirts and the giveaways will be revealed as soon as we have that done, definitely within the month.  !


The normal menstrual cycle and getting pregnant

In order to understand how birth control pills work, it is crucial to first understand the menstrual cycle.

In super brief:

The menstrual cycle is a complex interplay between hormones secreted from the pituitary gland, and the hormonal responses of the reproductive organs over the course of approximately one month.

In moderately brief:

In a normal menstrual cycle, FSH is secreted by the pituitary gland, which stimulates follicular development, then the ovaries respond with rising estrogen levels.  These estrogens then trigger an FSH decrease and an luteinizing hormone (LH) spike, which induces ovulation, and then progesterone levels rise.  Progesterone peaks and then falls, and the falling of progesterone triggers the shedding of the endometrium in blood flow during what we commonly call week 1.  Then the cycle begins anew.

In details: 

The first day of a menstrual cycle is the first day of bleeding.  During this period, the lining of the uterus is shed.  This bleeding constitutes the first 3-8 days of the first half of the menstrual cycle, which lasts about two weeks and is called the follicular phase.

During the follicular phase, levels of estrogen rise and make the lining of the uterus grow and thicken. Detecting elevated estrogen levels, the pituitary gland increases its production of follicle-stimulating hormone throughout the follicular phase.  This hormone stimulates the growth of 3 to 30 follicles.  Each follicle contains an egg.  With time, the levels of FSH decrease, so only one of the follicles continues to grow.  It produces estrogen, and other stimulated follicles break down.

Detecting this shift, the pituitary now releases luteinizing hormone.  This makes the follicle bulge and rupture, releasing its egg.  This is ovulation.  During ovulation, testosterone, which is otherwise constantly produced at low levels by the ovaries, surges, and estrogen drops.

After ovulation comes the luteal phase.  Here the ruptured follicle closes and forms the corpus luteum.  This thickens the endometriums, which in turn produces progesterone.  But if the egg is not fertilized within about two weeks, progesterone levels fall, which triggers shedding and bleeding.  Here the cycle begins again.  Cycles are generally “known” to be 28 days long, but the length of a regular, healthy cycle can vary from ~20 to ~35 days.

How a woman gets pregnant

A woman gets pregnant when a sperm is implanted in the egg in the dates immediately preceding, during and following ovulation (as much as a few days earlier if the sperm hang around long enough, and 1-2 days later, when the egg dies).   When this is the case, progesterone levels never fall.  Because progesterone levels never fall, menstruation never occurs.  This is why missing periods or “being late” is often the first sign a woman guesses she may be pregnant.


What birth control pills are

Birth control pills are streams of hormone supply.

They come in either a) progesterone-only forms, or in b) progesterone-estrogen combination pills.

They can be monophasic, diphasic, triphasic, or now quadriphasic, meaning that there can be a) a steady stream of a low dose, or b) a fluctuating amount of hormones.  This fluctuating, cyclical type of pill is thought to approximate a more natural cycle.

Usually birth control pills are taken in monthly cycle, and they deliberately induce menstruation, though now some formulations last for up to three months.

When to take the pill 

A woman takes a pill every single day for a given period of time, and usually at the exact same time.  This is important, because the level of hormones in the blood must be sufficient at all times in order to prevent a cascade of hormones further down the line.

Think of it like this: if you are late in taking your progesterone pill, your pituitary gland might get excited and send an LH signal.  You might later get the progesterone into your system, say 6 or 12 hours late, but by that time the LH has already been released, and ovulation has already occurred.  It is supremely important to take the pills on time.

How it works

Progesterone-only pills were the first pills ever designed.  The idea is simple, and the effect, profound.

Progesterone in the system– as we saw in the review of the normal menstrual cycle– prevents the release of FSH and LH in the brain.   In sum, that means that when a woman takes a daily progesterone pill, FSH and LH do not get secreted.  FSH and LH are responsible for ovulation taking place, so without them, the woman does not ovulate.

In greater detail, that means: in step 1) Progesterone inhibits FSH production.  Step 2) Low FSH levels prevent estrogen levels from rising, and prevent development of the endometrium.  3) Estrogen maintains a baseline low, and that fact, coupled with the high levels of progesterone, prevent LH from being triggered.  And finally, in 4) because there is no LH, no ovulation takes place. Because there is no ovulation, the woman does not get pregnant.

Combined oral contraceptives

Recently after the progesterone pill was developed, estrogen was added to several formulations to create the combined oral contraceptive. The reason estrogen was tacked on (a decade or so after the original development of the pill) was because doctors thought it would stabilize the endometrium and sort of prevent breakthrough bleeding.  Which it did.  What doctors found, however, was that the estrogen also helped prevent ovulation.  This is important to take note of for women who suffer from estrogen dominance and are trying to conceive.

The effect of adding estrogen to pills, then, is to prevent breakthrough bleeding.  It can also be helpful for women who struggle with low estrogen levels (often from low body fat or stress) or from high testosterone levels.  This is because estrogen helps balance testosterone in the bloodstream.  Women with PCOS, for this reason, are proscribed estrogen-containing pills much of the time if they are trying to manage their testosterone-dominant symptoms.

Other ways pills work

Birth control pills also have physiological effects that prevent pregnancy.  Progesterone decreases the amount of and increases the viscocity (thickness) of cervical mucus.  This makes it near impossible for sperm to penetrate through the cervix.

The timing of the pill

Most pills are designed to mimick as much as possible the natural menstrual cycle.    The reason for this is not quite clear, and leans heavily on the psychological.  When they were designing the pill several decades ago, doctors seemed to think women needed to menstruate regularly in order to feel normal or comfortable in their own skin.  That has changed in recent years, though that bias remains somewhat strong.

This fact means that the most common pattern is for progesterone to be taken for 21 days, and then either a placebo or no pill for the next 7 days.  By day 21 of the cycle, ovulation has already been inhibited long past.  This means that progesterone can be dropped off by day 21 with no worry of ovulation taking place, while simultaneously being enough of a drop to induce menstruation.

Another model is to change the 21-7 day cycle to 24-4 days, which can shorten and lighten the periods.

It is also physiologically somewhat important to have a withdrawal bleed, since it is possible that the endometrium will build up too thick without menstruation, which can lead to certain physiological complications such as cancer.  However, those occur on long time scales, and this effect varies widely depending on how much estrogen is in a woman’s system and how much her endometrium grows over time.

However, in general, the pill decreases endometrial thickening, so this is in fact a benefit of the pill–reducing the risk for this type and source of cancer– rather than a negative.

So is it necessary to have a withdrawal bleed every month?

No, in fact, it isn’t.

Some pills extend the cycle to three months long

Though the thing is, we can hardly call a three month long stasis a “cycle.”  It isn’t.  What happens in three-month long pills such as Seasonale is that progesterone continually inhibits LH and FSH without end.  No menstruation or cyclic pattern occurs.

Finally after three months– a somewhat arbitrary number decided on by pill manufacturers and the medical community, a withdraw bleed is induced by taking a few placebo pills. In theory, you could just keep taking progesterone and not menstruate for as long as you desired. But again, because it is nice to “reset” and also to clear up the endometrium, especially if on a pill that contains estrogen, withdrawal bleeds should happen occasionally.

Positive effects of the pill?

Reduction in cancer risk of female-specific cancers–endometrial, ovarian, and colorectal.

If this is true, it is probably in my personal opinion because of the dampening effect progesterone has on estrogen, which itself plays a role in feeding tumors.  However, other studies demonstrate increased breast cancer risk with pill consumption.

Increased vaginal lubrication?

Alleviation of PMS

Decreased Acne

Negative effects of the pill?

Increase in cancer risk (not yet known)

Weight gain

Decreased libido

Decreased vaginal lubrication



Psychological disturbances such as anxiety, insomnia, or rage


Pill acclimatization and amenorrhea

Another affect of going on the pill is that the body might become overly-dependent upon it. Hormones run off of negative feedback loops.  What this means is that detecting certain levels of a given hormone in the blood tells the appropriate glands to stop producing that hormone.  This makes sense, right, in light of the fact that the body wants to maintain proper hormonal balance.

This has negative implications for women who supplement with estrogen or progesterone (ie, take the pill) during their reproductive years, however.  Because the hormones are being eaten or injected into the bloodstream, the body often stops making them. And then after the pill, the body still does not make them. Some women might go several months or up to a year before they begin ovulating and menstruating again.

This is of course not usually the case.  Most women are just fine off of the pill.  Just as with the side effects.  60 percent of women report not having any side effects on the pill.  Most of the rest have some side effects, but bear with them. Others find that the side effects are unbearable, and choose other fertility methods.

Why the pill has both positive and negative effects

Each woman’s body is different.  This means that adding estrogen to the bloodstream might help her symptoms, but in other cases adding estrogen to the bloodstream could do a lot of harm.  The same of course goes for progesterone.  Adding these hormones to the bloodstream has the potential to either increase or decrease the levels above what is natural for a woman– and in fact it is almost certain that they will be differently balanced.

Upsetting the natural balance between estrogen and progesterone, as well as between those hormones and the rest of the sex hormones, particularly testosterone, can have serious effects on a woman.  Estrogen and testosterone need to be specifically and well balanced in order for a woman to have a properly functioning sex drive.  Estrogen and progesterone need to be well-balanced for clear skin.  And so on and so forth.  The list is long.

It is worth noting, moreover, that estrogen and progesterone act as “antagonists” to one another, meaning that progesterone has the power to reduce estrogen’s effects, and vice versa.  This is partly why combination pills are desirable for many women, though it is also why estrogen-dominant women might choose a progesterone-only pill.

That being said…

The pill is complicated!  In my personal experience, it’s just not worth it.  But the negative health effects of the pill are all specific to the individual.  As are the positive effects.  And long term health impacts are not well-understood.  For that reason, it is entirely specific to your body and your needs whether or not getting on a hormonal regimen is “worth it” for you.

As a final note…

As a result of the pill, women are excreting more hormones than usual, which are making their way into the water supply.  This has significantly disrupted the reproductive cycles of some fish.  It is also questionable how much these products make it into the water supply.  Most studies seem to show that small percentages of it do (between ten and twenty percent), but that water treatment plants are mostly effective at filtering them out.


What I listed above are well-known and popular effects of the pill.  What was your experience?  Did you have any side effects?  Any unusual side effects?  Let us know!  The pill can do a whole lot more than it is commonly accounted for.

And remember to check out Birth Control Unlocked for even more information on the pill.

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