Almost 50 years ago the combined oral contraceptive pill was approved by the Food and Drug Administration (FDA) for use in preventing pregnancy, ushering in a new era of hormonally-based birth control. Now, in addition to the original “Pill” women can chose from an overwhelming variety of oral contraceptives, from different hormone combinations and doses to different Pill schedules that result in skipping or stopping menstruation entirely. Most of us have heard that the Pill contains hormones that suppress ovulation, but how does this really work? And with the recent marketing of Lybrel — a Pill designed to stop menstrual cycling entirely — we might wonder how far we can reasonably take this hormonal control. Simply put, how does the mechanism of oral contraceptives guide us in their use, and what (if any) are the repercussions of eliminating menstruation?

The story of how the Pill was engineered to suppress ovulation is one of the first examples of researchers using naturally occurring hormones to re-direct normal human biology. As far back as the 1920s, scientists had determined that transplanting ovaries from pregnant rabbits into other fertile rabbits prevented pregnancy, and by the mid-1940s it was known that the hormone Progesterone was responsible for this effect. Researchers then wondered: What is the role of Progesterone and other hormones in regulating normal reproductive biology, and could this knowledge be safely used to suppress ovulation in humans?

How does the Pill work?

Before pills could be formulated to modify human ovulation, researchers needed to figure out how the menstrual cycle usually works. The normal cycle consists of several distinct phases that average approximately 28 days in total; each phase corresponding to physical changes that occur to “build up” and “break down” the uterus in preparation for pregnancy, with ovulation occurring at the midpoint of the cycle. These phases are associated with dramatic changes in the levels of certain hormones that follow carefully scripted roles in promoting ovulation and subsequently (in the absence of fertilization) menstruation.

The shedding of uterine lining leading to the observed bleeding is the Menstrual Phase. As bleeding ends, Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) show small peaks above their normal low levels, leading to thickening of the uterine lining and maturing of oocyte(egg)-containing follicles in the ovary. Meanwhile, the estrogen, Estradiol (E), is steadily rising to a peak a few days before ovulation, after which point FSH and LH spike once more, triggering the release of a mature oocyte. Levels of Progesterone (P) and E rise for the next two weeks, preparing the uterine lining for implantation of an embryo. If no implantation occurs, both hormone levels drop sharply, triggering menstruation. If fertilization and implantation do occur, levels of P and E remain high throughout pregnancy, suppressing the spikes of FSH and LH that drive ovulation.

Because of the intricate feedback loops controlling the menstrual cycle, artificially altering one or two hormones can affect the entire cycle. This fundamental knowledge has been used both to suppress the cycle, with the goal of contraception, as well as to stimulate ovulation with the hopes of promoting fertility. Two ideal targets for hormonal contraception would be the hormones FSH and LH, which play dual roles in the normal menstrual cycle, first re-starting the cycle after menstrual bleeding and then triggering ovulation at the mid-point of the cycle. Because FSH and LH are required to trigger ovulation, artificially blocking these two hormones would therefore robustly suppress ovulation. Why then are the hormones P and E commonly used in the Pill instead? It is generally easier to add something to a biological system than to remove something, and since P and E suppress the release of FSH and LH these are logical choices for halting the sequence of events that lead to ovulation. Because both P and E are at high levels throughout pregnancy, some people describe taking the Pill as “tricking the body into thinking it’s pregnant”. While not entirely accurate, this statement does have some truth to it.

How well does the Pill regimen mimic the normal menstrual cycle?

The standard combined oral contraceptive consists of both hormones P and E, taken daily for three weeks, followed by a week of no pills (or placebo pills) that trigger what’s known as “breakthrough bleeding”, induced by the drop in hormones. Although the outward appearance is the same (menstrual bleeding in week 1 of a 28 day cycle) the constant high levels of P and E for a woman taking the Pill actually abolish the normal hormonal cycling that underlies ovulation. The Pill therefore replaces the normal menstrual cycle with an artificial cycle (3 weeks of “mimicking pregnancy”, followed by 1 week with breakthrough bleeding). Historically, women have been pregnant or nursing much of their adult lives and thereby suppressing ovulation naturally, suggesting that halting menstruation is not inherently harmful. Yet, many women still wonder if it is safe to eliminate menstruation using oral contraceptives.

Actually, women have been using the Pill in this off-label manner under medical supervision since the time it debuted — skipping the week of placebo pills in order to postpone their periods during a vacation or special event, for example. Continuous menstrual suppression via the Pill has also been used to treat endometriosis, debilitating menstrual pains and other menstruation-related ailments. However, it is only recently that certain formulations of the Pill began to be marketed for the specific purpose of eliminating periods. The first widely available Pill of this nature was Seasonale, FDA approved in 2003. Each packet of Seasonale contains 84 Pills and 7 placebos, resulting in 4 periods per year. In 2007, the Pill, Lybrel, was introduced, eliminating the placebos entirely with the goal of suppressing menstruation as long as the Pill is taken. So, although at first glance it may seem unusual to provide an oral contraceptive regimen that eliminates periods, the use of Seasonale, Lybrel and other similar formulations is a logical progression from the original concepts behind the Pill. These new formulations contain the same types and amounts of hormones as the standard Pills, so should be comparable in terms of side effects (both immediate and potentially long-term). However, the lack of menstruation does mean that a woman who becomes pregnant on this regimen may not realize it as soon as she otherwise would. How popular this newly-advertised birth control regimen will be (given that it removes the visible monthly proof of its efficacy) remains to be seen.

–Amanda Nottke, Harvard Medical School

For More Information:

Information regarding the FDA’s approval of the prescription drug, Lybrel:
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Science Daily article about menstruation suppression using oral contraceptives:
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Primary Literature:

“A Short History of Oral Contraception” Wolfgang Oelkers, The Endocrinologist, Issue 80, p.15.

17 thoughts on “Taming the Cycle: How Does the Pill Work?

  1. I am speechless. The scientific community is pushing for even more extememe measures of female hormonal birth control, yet we don’t even have male birth control (i.e. Vasalgel, that is non-hormonal and aims at no unwanted side effects) out in the U.S. market yet. This just goes to show how Big Pharma just loves to capitalize off of female birth control because they know that it will sell. This just goes to show such a gender disparity when it comes to birth control–this creates such an unleveled gender playing field.

    Women are expected to suffer the side effects of hormonal contraceptives, yet we can’t even find options for men?

    Again, I am speechless…

    I am utterly disappointed at America’s current state of healthcare affairs, escpecailly when it comes to dealing with women’s health issues. Women do not have quality healthcare at all.

    Nice article, by the way. Perhaps focus more on the issues I’ve lined above?

    1. This isn’t an opinion piece…it’s just an objective explanation of how the combination pill works. If you insert those sorts of opinions into a medical text it lowers it’s credibility because critical thinkers will ask, “what motivated you to include this, the facts, or a desire to achieve some sort of justice?”

    2. Long ago when I used the pill, it made me moodier, more bloated, gave me bad headaches, cramps were worse, & I hated how I felt overall using them. I was so glad the day I finally DITCHED them & never went back to them. They can & do act as abortifacients. The reported benefits of the use of these pills did not apply to me at all.

      Using the pill has lasting, damaging, & observable environmental effects that have been documented.

      Read the following articles:

      ScienceDaily: “Estrogen in birth control pills has a negative impact on fish” (March 4, 2016)

      Scientific Reports: “Transgenerational effects from early developmental exposures to bisphenol A or 17α-ethinylestradiol in medaka, Oryzias latipes” (20 March 2015)

      Washington Post: “With funding scant, intersex fish in Potomac remains mystery” (November 24, 2009)

      USGS: “Pharmaceuticals, Hormones, and Other Organic Wastewater Contaminants in U.S. Streams, 1999-2000: A National Reconnaissance” (1-1-2002)

      NCBI: “Collapse of a fish population after exposure to a synthetic estrogen” (2007 May 22)

      Wisconsin Watch Website: “The hunt for endocrine disruptors” by Kate Golden (May 19, 2013)

      It appears that we now have more things to consider than just our sex lives.

    3. Completely agree with Alex. Takes away the scientific feel of this informative writing.

      Heck, this article saved my end of semester review essay!

    4. Birth control pills are also used to treat other conditions women suffer from. I have endometriosis and having periods is not an option for me. The only way that I can live my life is to continuously take the pill with no off weeks. So it’s not just a gender issue. There are actual health issues here as well. And, I would be forced to have a hysterectomy at age 29 if it wasn’t for these advances in birth control
      I only hope that more advances in endo treatment come soon

    5. If you don’t like it, don’t use it. We are the ones to carry the baby, so it is primarily our concern. Since men do not have such a repercussion from intercoarse, they are not as concerned. It makes logical sense that I would be (being female) more concerned what happens to my body and in charge to control it the way I desire.

  2. I’m a 19 year old male and I think it’s horrible that woman have to use birth control and men don’t as soon as male birth control is on the market I’m gonna drop everything and run to the doc

  3. The information given in the above article are just amazing and interesting. I have also read about “Necon Birth Control Method” – Modern method of controlling birth now a days accepted by a large number of people in World. I also read about advantages and disadvantages of this method.
    It is my humble request please read the article and let me know that information given here is truly genuine or not. I have read the article from this site:

  4. For so many days i was in search of best birth control method than I come to watch this post about working of birth control pill, I also read the “side effects of necon birth control pills” from the following link. Can anybody please tell if these side effects are genuine or not. Thanks in advance.
    Necon Birth Control Method

  5. I really wonder how young you can be to take birth control. I’m only 12 and have just started my period last month and I hated it! People keep saying to me that it might change and you will never know what will happen but that just makes me more nervous and also makes me think should I ask mom if I could take birth control? I really hated my cramps and everything about it. Cramps were so bad I was hysterically crying to my mom about how bad they were and personally
    I think if I started taking birth control it could possibly help with all those horrible cramps. I’m so young and if I take birth control will it really effect me? My mom takes birth control and she’s completely normal but it works different for many people so what if it works really bad and starts making thing more bad for me. I’m really caught up with this situation so if you have any advice can you help. Thanks.

    1. Yes you can start take birth control as soon as your periods started. But it’s better to talk to your doctor or nurse first

  6. Hey this was a great article. It was written with both a scientific and lay-person’s voice which makes it easy to read. Sorry for the first comment, this was a historical piece, not an opinion piece. I don’t think you intention was to provide a political stand-point for or against the use of these pills.

  7. Hi. I’m sixteen, and my menstrual cycle is once every 28 days. But according to the Baby Centre website, ‘A normal menstrual cycle could be as short as 22 days or as long as 36 days.’ Since your cycle is 2 days longer than the normal menstrual cycle listed there, perhaps you should see a doctor, just in case. Every woman’s cycle is unique, so to be honest, it’s best to get it checked from

  8. Hello. I am 28 years old and my menstrual cycle is 28 days. But according to the Baby Center website, I want to know what the difference between the menstrual cycle between each woman depends on?

  9. It’s really a cool and helpful piece of info. I’m satisfied that you just shared this useful info with us.
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  10. Thank you for this article. It was a super informational and helped me lot. Please keep this kind of content coming. I will follow your articles on forward.

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