Basic Set: Female Reproduction 3, Oral Contraceptives

Feb 24 2010 Published by under Basic Science Posts

Continuing in our vein of basic science posts on female reproduction, we're going to take a bit of an aside (and this is VERY relevant for the paper that Sci wanted to blog about that needed so much background). We've covered the basic anatomy, the hormones, and the monthly cycle. But what about...when you don't want to ovulate?

What about oral contraceptives?

Of course, they aren't all oral anymore. Now we've got the patch and the ring, and I'm sure pretty soon we'll some sort of nasal insert (maybe something that looks like a nose ring?) for those who cannot be bothered with either a patch or a ring, let alone a pill.

So what about these?
the Pill

the Patch

(I do seriously hope they make the patch in darker tones than that. I do not think it would be hard to make a patch that actually matches your skin tone, so I really hope they market them)

the Ring


(on the other hand, if you wanna make me a birth control absorbed through the skin that can be worn as a RING, and make it to look like the One Ring, I WILL wear it. Drug companies, take note.)

So, remember this?

Of course you do! Excellent. Let's go.

As you can seen above, increases in estrogen (occurring in a stepwise fashion) occur throughout the first 11 days or so of the cycle, only to drop off massively right before ovulation. This drop-off actually TRIGGERS the surge in LH and FSH, which in turn cause ovulation.

So if LH and FSH surges are required for ovulation, what should you do to prevent ovulation? Stop the surge obviously. And HOW exactly does the pill do that?

The pill has many formulations, but most contain synthetic estrogens and progestins, and some contain only progestin. What they do is keep the levels of circulating estrogens and progestins HIGH. If you keep the levels of circulating estrogens high, you avoid that big drop at day 11. That big drop prevents LH and FSH from increasing, which prevents ovulation. Deceptively simple. Looks like this:


On the top you can see the normal menstrual cycle, this time with LH and FSH on top and estrogen and progestin on the bottom. This picture shows a progestin only oral contraceptive. You can see on the bottom that the progestin levels are kept high, and this means the Lh and FSH (green and yellow lines) never spike (see third panel).

Of course, you need to be careful. You don't want to give super high amounts of hormones (there are worries about cardiovascular problems and cancer here), the goal is to give just enough that the body doesn't notice the usual drop in estrogens, and fails to release LH and FSH. The lowest dose possible is often considered best, and this has actually become something of a problem due to rising weight in the US. When people are of higher weight, they need to take higher doses to prevent ovulation, and a lot of times, the pills are only made for a weight within the "average" range.

However, even if you DO ovulate despite your birth control (for the progestin-only pills, you still ovulate roughly 50% of the time), there's still little chance that you will get pregnant. Why, you ask? Because higher levels of estrogen and progestin have another effect on the body. They thicken the vaginal mucosa (yer fluids). This thickened mucosa is no fun for sperm to swim through, and makes it much more difficult for fertilization to occur. It's nice to know there's an extra barrier there, just in case.

Wait. If you don't ovulate (usually) on birth control, why do you menstruate? Well, technically speaking, some physiologists don't believe you need to. It could be possible for you to go some time without menstruating if you're not ovulating, and this is the idea behind the three-month birth control types like Seasonale. However, many people still feel more comfortable menstruating every month.

So every month, when you've gone through three weeks of the birth control packs, you keep taking pills, but you menstruate anyway. What happened? The pills you are taking during that week are actually placebos (or, in the case of the ring or patch, you take it off during the days you are supposed to menstruate to stop the hormone influx). They don't contain any estrogen or progestin in them, and when the estrogen and progestin levels drop off (as at the end of a normal cycle), your body does its usual thing and shed the endometrial lining, and you menstruate. For the progestin only pills, there is no break between packs (no placebos), as a constant dose of hormone is needed to prevent ovum development. This also means that progestin-only pills have to be taken much more consistently than the combined estrogen/progestin types (estrogen/progestin types can take a leeway of up to 12 hours, progestin-only has a leeway of 3 hours).
Placebos, did you say? I'm taking placebos!?! Does that mean that I can get pregnant if I have sex during my period? Nope. Because if you were taking the pills on time for the rest of the month, you haven't ovulated. There's nothing there to fertilize.

Keep in mind, though, that oral contraceptives should NOT be skipped. You're still getting a dose of estrogens every day. If you miss a pill or two, the estrogen levels will DROP sufficiently to cause that surge in LH and FSH, leading to ovulation. So if you don't want that to happen, don't skip.

Side Effects

weight gain: A couple of studies found that people didn't like the pill because it caused weight gain. That was a study done in 1998 in 15-19 year old girls. However, the vast majority of studies have found that the lower doses of the pill do not have significant weight gain problems associated with them unless you are having an unusual reaction. Some scientists think that women notice weight gain when they start taking the Pill because of WHEN they start it. For example, when you go to college, when you start puberty and start putting weight on, when you get married and move in together, etc. But the scientific consensus is that combined oral contraceptives (like the pill, patch, or ring) do not cause weight gain above normal. Some weight gain IS seen with the progesterone only formulation when given as an injection or IUD. Some women will notice increases in breast size and tenderness during the first few weeks. The tenderness usually goes away. The size often stays. Some women don't mind this, but some do. Up to you.

acne: The pill is sometimes prescribed to help with acne, by evening out the hormone fluctuations that result in monthly breakouts. In some rare cases, it can make acne worse, but most of the time we think it makes it better.

heart issues: The pill can change blood clotting, cause higher blood pressure, and increase the odds of things like stroke and heart attack. Keep in mind though, the risk is VERY small, and if you're young and healthy, you're probably fine. However, to reduce the risks, some women prefer the ring. Because it goes up inside the vagina, the local levels of hormone are more effective and the circulating blood levels of hormone don't need to be so high. OTOH, it's a ring up in your vagina, with some people find rather inconvenient.

Other complaints: studies vary on libido, some women find their libido is better because they aren't so worried about getting pregnant, others find it's worse. The pill can also worsen symptoms of depression, particularly the progestin only varieties, but scientists are divided on this point as to whether or not it's a very common side effect, or more rare.

And that's my aside on how oral contraceptives work. Next time, it's back to the female reproductive cycle. Get ready for Pregnancy!

16 responses so far

  • Kirsty says:

    I know anecdotal evidence isn't true evidence, but I'm one of those that experienced the depression side effect. So much so that none of the contraception options above are viable options for myself, nice to know I may be one of the rare few. It is also common for female depressives to experience symptoms shifting in tune with hormonal cycles.
    I've been enjoying your posts on Female Reproduction!

  • Lab Rat says:

    "It could be possible for you to go some time without menstruating if you're not ovulating"
    Yep...I've done that. I take the double pill (two hormones) and occasionally if I'm hiking, or insanely busy, or it's valentines day, I'll run onto the next packet without taking the week off. Once had four months without a period by doing that, although the cramps for the period after that were *insane*.
    Nowadays I tend to run one month on, one month off, although I have no idea whether that's supplying me with slightly too many hormones or what. When I ask at the pharmacy I only get woo answers 🙁 ("Oh but it's *natural* to have a period, you probably *should*")

  • anna says:

    Apologizing in advance for no links, there is a great article I read in one of the "Best Science Writing of (year)" books a few years ago about the development of The Pill and its inventor. As a Catholic, his idea was that in order to practice the "Only Acceptable Birth Control", the rhythm method, one needed to have a reliable rhythm. Hence the 3-week-on, 1-week-off formulation. Eventually of course once the science behind it was understood it became the obvious contraceptive choice, but retained the original 3-1 design.
    Again, no links, but there is also some thought regarding the number of periods "necessary" in a woman's lifetime, and that we have far more today then the average woman did in the past. This is based, as I recall, on estimating historical age of menarche onset, estimated number of pregnancies, months lactating, etc., which would reduce the number of months menstruating compared to a nulliparous or single birth woman of today.
    Perhaps someone could ferret out the info. Maybe I'll have time today.

  • DNLee says:

    no, that dern patch does NOT come in other tones. AND to make it worse, it's not highly effective or recommended for Big girls. But I LOVE Nuvaring. It's the best BC I ever tried.

  • Scicurious says:

    DNLee: Are you KIDDING ME?! No wonder the model is looking at the camera as if to say "Really? I mean, REALLY?!" How hard is it to make it a little darker?
    The weight issues are becoming more common with both the pill and the patch. It's not such a big issue with the ring, as the ring is more local and thus weight is not such a problem, but with systemic drugs like the patch and the pill, they tend to be designed for a certain weight, and for those who are heavier, the dose might be too low (conversely, for those who are lighter, it might be too high, and result in more side effects). Sci thinks it wouldn't be such a big deal to create a range of doses for different sizes of women, which might help keep the birth control more effective.
    Anna and Lab Rat: right, there's not a lot of evidence out there on whether menstruating or not is better. Many people do worry that stuff will build up in there or something, but that's kind of silly. The blood and serum you slough off every month (or so) is supported the rest of the month by extensive capillary networks, so it's not like it's just rotting in there. Many people do think it's a good idea to menstruate every month for "insurance". But Lab Rat, I wouldn't ask your Pharmacist, I'd ask your doctor. Pharmacists often aren't trained in this sort of thing.
    Kirsty: yes, some women do have depression that cycles with their hormones, and in those cases, birth control can make it worse. However, many other women have depression that is independent of hormone cycling, and often it's hard to differentiate between the two, so they can't really say whether the side effect is common or not.

  • nikipedia says:

    Correct me if I'm wrong, but I think it is not entirely accurate to say that the pill keeps your body at a high hormone level (but it is hard to argue with graphs!). I have done salivary assays for 17beta-estradiol and progesterone, and women on the pill have drastically decreased levels of both of these.
    If I understand correctly, the synthetic estrogens and progestins in the pill have a higher binding affinity than the endogenous versions of the hormones. So relatively small doses of these guys take up all the receptor real estate and send negative feedback to the endogenous system, leading to a net decrease in circulating estrogen and progesterone levels.
    Also, I believe the improvement in acne tends to be attributed to a decrease in androgens, another side effect of the pill.
    And one more also: I don't for a second buy the stuff about the pill not affecting depression. The existing literature is sparse and riddled with contradictions. The most compelling explanation for this I've heard is the idea of a "survivor effect" -- some women have no mood change in response to the pill, some have a positive mood change, and some have a negative mood change. Only the first two groups are likely to keep using it.

  • Jefrir says:

    estrogen/progestin types can take a leeway of up to 12 hours, progestin-only has a leeway of 3 hours

    This is a little out of date: the progestin-only pills I was on about 4 years ago could be taken within a 12 hour window. They were apparently fairly new out then. The trade name was Cerazette, I believe.

  • Scicurious says:

    Jefrir: It's true that there are one or two brands that are good for 12 hours, but as far as I know, there are only those one or two. In general the progestin only pills have a short window.
    nikipedia: I didn't mean to say that the hormone levels are HIGH, as in astronomically high, just that they are higher than normal, high enough that the drop in estrogen isn't detected and FSH and LH are not released. The graph is just a representation, and I don't think it's accurate (esp as there is no Y axis there). Also, you are right that if women are on synthetic estrogens, it makes sense for their natural estrogen and progestin levels to be low as past of a negative feedback. I'm afraid that I don't know the binding affinities for oral contraceptives off the top of my head.
    And Re: depression, I don't buy ANYTHING until the literature tells me something. So I won't say one way or the other.

  • brand0con says:

    Anything to add about the possibility that attraction patterns change while on birth control? I've read that attraction to a certain set of (quite possibly pseudoscientific) pheromones is reversed in some women due to the hormonal changes brought on by BC.

  • Katherine says:

    This is just anecdotal, but different brands of the pill with different synthetic hormones in can have different side effects on different people. Both my sister and I were depressed on one brand, but we both found brands that worked for us in the end. This might not be something that everyone has heard of so I thought I'd put it out there. Of course this may not help everyone, but don't despair because the first brand you try gives you bad side effects (unless you live in the US and that brand is the only brand your insurance will pay for 🙁

  • darchole says:

    Weight has an effect on the shot (depo-provera) too, if the woman has more body fat it might not be injected in the right place (can't find a citation for it right now, but I think the injection has to be IM and not ID?)
    Sci - it depends on the MD but in my experience, most aren't trained to appreciate that "no evidence" does NOT mean "natural is better" in the birth control and frequency of periods debate, AND they never discuss that fact with their patients. So for most women it's not choice, but the feeling they have to have a period because it's medically necessary and not because they choose too because they have all the facts, or theories.

  • Steph says:

    I'm not sure if this is the article you read, but it's a fascinating account of the history of the pill, and he talks about the increased number of periods in a woman's lifetime:

  • [...] when women are cycling normally. What about when they’re NOT? What about when they are on the pill? So in this study, the scientists compared gray matter volumes in men, women without oral [...]

  • [...] CAUSATION. There are many reasons why one might gain weight about the time that one starts taking hormonal contraceptives. Examples of this include: moving off to college, beginning a different style of life, or simply [...]

  • Demelza says:

    I'm impressed by your writing. Are you a perfossional or just very knowledgeable?

  • Marie says:

    Interesting article! Regarding depression while on the pill, I appreciate that the literature may not be conclusive, but there is probably considerable bias in reporting at least in clinical practice. For example if a woman goes to her GP with depression, the GP may not necessarily ask if she is on the pill. It's likely she'll just be prescribed antidepressants and sent on her way, and she'll continue to take the pill alongside the antidepressants. Whereas if women were routinely asked this question when presenting with depression, and a trial period of coming off the pill was suggested for depressed women, we may see more of the true picture of how the pill affects depression.

    All the combined pills I've tried have listed 'severe depression' on the label as a potential side effect. Even so, I have found that GPs are very reluctant to recommend that a woman comes off the pill, presumably because of the risk of unwanted pregnancy. During a recent depressive episode I was scolded by my GP for wanting to try coming off the pill - but I did it anyway, and my depression lifted.

    My point is that I wonder how many women just quietly stop taking the pill, or end up being prescribed antidepressants, and so the link is never made? There is a reporting system for side effects (in the UK at least) but it isn't widely publicised and I'd like to bet very few people know about it or use it.

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