How the Birth Control Pill Works

The pill: the choice method of contraception for more than 11 million women in the United States.
The pill: the choice method of contraception for more than 11 million women in the United States.

­If, 100 years ago, you told a woman that one day women would be able simply to swallow a tiny pill to avoid getting pregnant, she wouldn't have believed you. In 1909, condoms had already been in existence for hundreds of years, but depending on where you lived, they weren't always legal. Even if they were legal, they might not be culturally acceptable, affordable or reliable. Other than avoiding sex completely, the only other option a woman had might be the use of herbs or other folk methods. And those weren't always reliable, either.

The oral contraceptive pill, known simply as "the pill," is a marvel of modern chemistry. It's the most popular form of birth control in the United States. More than 11 million women reported using it in 2002 [source: CDC]. Today, it's legal, culturally acceptable, affordable and reliable. But it didn't come by all of those attributes so easily. The pill was first approved by the Food and Drug Administration (FDA) as a contraceptive in 1961, but until a 1965 Supreme Court ruling, only married woman in some states could obtain it. Until another Supreme Court ruling in 1972, unmarried women in some states still couldn't legally get it.



The pill is pretty straightforward on the surface. A woman takes one pill at the same time each day for 21 days. Then she either takes an inert pill (a placebo meant to keep her in the routine of taking a pill each day) or takes nothing for seven days while she has her period. Because the hormones in the pill keep her from ovulating, she shouldn't get pregnant.

The truth is, though, that some women who are on the pill do become pregnant. Some women experience side effects so unpleasant that they have to switch between different types of the pill or stop taking it altogether. And although it has been legal and available to all women since 1972, they might still have trouble obtaining it. Despite its popularity, the pill hasn't been without controversy throughout its history.

Let's start with looking at exactly how the pill works in a woman's body to prevent ovulation.




Getting Hormonal: Overview of the Menstrual Cycle

The pill keeps women from getting pregnant because the menstrual cycle is controlled by hormonal changes in the body. Let's take a look at the menstrual cycle.

Although its actual length can vary from woman to woman, the menstrual cycle is generally 28 days long and follows a few basic phases that are all triggered by the release of different hormones.



First, the pituitary gland sends out follicle-stimulating hormone (FSH). Just like the name implies, FSH stimulates follicles in the ovaries to grow. The follicles release the hormone estrogen, which sets off a chain reaction. Estrogen triggers the pituitary gland to secrete gonadotropin-releasing hormone (GnRH), which in turn triggers a rise in the secretion of luteinizing hormone (LH). Generally, one of the ovarian follicles dominates the others in size and growth. Estrogen and LH continue to rise, which prompts the uterus to build up its endometrium, the thickened uterine lining, and causes changes in the vaginal mucus that make it a better environment for the sperm.

A rise in LH causes the dominant follicle to mature into an ovum, or egg, while the immature follicles dissolve. The egg releases from the ovary (a process called ovulation) and enters a fallopian tube. If it goes unfertilized, the egg eventually dissolves. If sperm are present, the egg may be fertilized in the fallopian tube. Then it travels down into the uterus and implants in the endometrium. After the egg is released, a structure in the ovary known as the corpus luteum produces hormones such as progesterone and estrogen. These hormones help make the endometrium suited for the egg's implantation and cause changes in the uterus to support the egg's growth.

Next, we'll look at what the hormones in the pill do.

Hormones and the Pill

The hormones in the pill, progestin (which mimics progesterone) and estrogen, decrease the release of GnRH, and therefore the release of FSH and LH. This restricts the follicles from growing, and by extension, an egg from growing and releasing from the ovary. Essentially, these synthetic hormones trick the ovary into thinking that it's already released an egg. The endometrium still builds in the uterus and is released, but this is known as a "withdrawal" period. It's the body's reaction to the withdrawal of the normal hormonal cycle. This is why a period while on the pill is usually lighter and shorter; the corpus luteum can't grow unless the ovary has released an egg. The progestin may also make it harder for sperm to enter the fallopian tube by making the vaginal mucus thicker.

You'll notice that the pill doesn't completely stop the release of GnRH or other hormones. This is an important distinction. While it's not common, some women who take the pill still ovulate and become pregnant. Most often, it's because they didn't take the pill at the same time each day or missed one or more pills. In general, the pill must be taken consistently and regularly to maintain the correct balance of hormones. For a small number of women, their own hormones are no match for the synthetic ones used in the pill and they still become pregnant. Among women who take it correctly, the pill failure rate is 0.3 percent [source: Contraceptive Technology].



All women are different, which is why the pill works to varying degrees of effectiveness. Some also experience side effects. We'll look at these next.

Birth Control Pill Side Effects

In addition to preventing pregnancy, the pill can have all sorts of side effects -- some negative, some positive. The most common side effect of the pill is breakthrough bleeding or spotting, which is when a woman bleeds in the weeks she's taking active pills. This is due to the changes in hormone levels. Most women's bodies adjust after a few months of being on the pill.

Other common side effects include:



  • nausea
  • headaches
  • breast soreness
  • acne
  • decreased libido
  • depression
  • moodiness
  • weight gain

Many of these symptoms are due to the estrogen in the pill. Sometimes they go away after a few cycles, but if they don't, a woman might need to switch to a different formulation.

The pill also carries some more serious, although rare, risks. Taking the pill increases a woman's risk of high blood pressure, blood clots, strokes, heart attacks, liver tumors and gallstones. Some of these conditions can be fatal, but the risk of experiencing any of them is very low.

A woman is more at risk if she's overweight, older than 35 years old, smokes, has diabetes or already has high blood pressure or high cholesterol. Some studies have linked taking the pill to an increased risk of breast and cervical cancer, while others show no increased risk. The most recent theory is that the increased risk is temporary and only occurs within the first five years of taking the pill, when the risk of contracting these types of cancer is already very low. Women who stop taking the pill eventually go back to having the same risk factors for these cancers as before.

But the pill can also reduce cancer risk: A January 2008 study in the medical journal The Lancet showed that the longer a woman took the pill, the lower her risk of ovarian cancer.

For many healthy women without risk factors, the benefits of taking the pill tend to outweigh the risks. Women on the pill often report shorter, lighter menstruation, fewer and less painful cramps and better skin. The pill can fix irregular periods, reduce iron deficiencies (as less blood is shed during menstruation) and reduce the risk of benign cysts in the breasts or ovaries.

Women with polycystic ovarian syndrome (PCOS) and premenstrual dysphoric disorder (PMDD), an extreme form of PMS, can also find relief from some of their symptoms by taking the pill

We've been talking about "the pill," but the truth is, there are many pills. Next, we'll look at the differences between them.

Types of Birth Control Pills

There are three different types of oral contraceptive pills: combination, progestin-only or extended-release.

The combination pill is the one most commonly used, but the progestin-only pill, also known as the "minipill," is a better choice for some women -- women who are breastfeeding, for example, can't take a pill with estrogen because it affects their milk supply. Some examples of minipill brands include Micronor, Femulen and Microval.



The minipill prevents pregnancy in two ways: It makes the endometrium too thin to accept a fertilized egg and makes the vaginal mucus too thick to allow sperm to reach the egg. It's slightly less effective than the combination pill, and women taking it are more likely to experience spotting. Taking the minipill means taking 28 active pills every month, and it's even more important to take it on time to avoid the risk of pregnancy.

As far as the combination pill goes, there are three main subtypes:

  • Monophasic pills have the same amount of hormones in all 21 pills. They're the most commonly prescribed combination pill because they're very simple to take -- they're all the same color, and if a woman misses one, she can easily double up the next day. Some brand names include OrthoCyclen, Alesse and Loestrin.
  • Biphasic pills alternate between two different levels of hormones and are lower in hormones overall. Examples include Mircette and Ortho Novum 10/11.
  • Triphasic pills alternate between three different hormone levels. Tri-Levelen, Ortho TriCyclen and Triphasal are some examples.

All types contain 21 active pills. (Some brands also include seven days of inert pills to be taken during the week of menstruation.) They all contain the same type of synthetic estrogen, called ethinyl estradiol, but vary in the type of progestin they use. The main difference is that some women who experience unpleasant side effects on monophasic pills might do better on biphasic or triphasic pills.

Rather than wait seven days between active pills, some women simply start over with the 21 day pill cycle when on a monophasic pill to avoid having a period.

Next we'll look at the newest type of the pill.

Extended-cycle Birth Control Pill

The newest type of pill is especially designed for continuous use. Sometimes known as the extended-cycle pill, it either reduces the number of periods a woman has or eliminates them completely. The three brands currently on the market are:

  • Lybrel - 365 days of pills, resulting in no periods at all
  • Seasonale - 84 days of pills, 7 days of inactive pills, resulting in a period four times a year
  • Seasonique - 84 days of active pills, 7 days of lower-dose estrogen-only pills, resulting in a period four times a year

A health care provider might prescribe extended-cycle pills for a woman who has painful periods even on typical combination pills, or for someone who just wants to avoid the inconvenience of a monthly period.



Extended-cycle pills can be more effective than combination pills and better at treating some disorders like chronic benign cysts, endometriosis and PMDD. These types of pills carry the same side effects as combination pills but are more likely to cause spotting. They may also cause concern among fertile women because there are fewer periods, or none at all, to serve as an indication that they're not pregnant.

Although it may seem unhealthy to limit or go completely without a period, it isn't. The constant levels of estrogen and progestin keep the uterine lining very thin, so there isn't really anything to shed anyway. For the whole story, read Do you really need a period every month?

The pill generally costs between $20 and $50 per month. Most insurance plans cover the pill, and older brands and generics are usually less expensive. The extended-cycle pills cost more because more pills are taken per month. Family planning clinics and local health departments often distribute a pill supply for six months or longer at a reduced rate.

Margaret Sanger, Feminism and the Pill

Although she's also known as a highly controversial figure for her avocation of eugenics, it's safe to say that the birth of the pill started with Margaret Sanger, founder of Planned Parenthood. In 1912, Sanger, a nurse, wrote about the possibility of a "magic pill" that women could take to prevent conception. In her work, she saw many women who died or were injured as a result of self-induced abortions and others who suffered from the health effects of multiple childbirths. Not only would the magic pill improve women's health both physically and mentally, Sanger reasoned, it would also allow them to find more enjoyment in sexual intercourse because they could decide when and if they wanted to become pregnant. In 1914, she began writing a newsletter called "The Woman Rebel" in which she coined the term "birth control."

In the late 1920s, scientists identified both progesterone and estrogen and became aware of their roles in conception and pregnancy. Research into the possibility of a medication to prevent ovulation began in earnest, but it was initially too expensive to order the hormones, then synthesized from animals. In 1941, Dr. Russell Marker discovered a way to synthesize progestin (the synthetic form or progesterone) from wild yams, making research more affordable.



History of the Pill

American social reformer and founder of the birth control movement Margaret Sanger at the Neo-Malthusian and Birth Control Conference in New York City
American social reformer and founder of the birth control movement Margaret Sanger at the Neo-Malthusian and Birth Control Conference in New York City
General Photographic Agency/Getty Images


In 1950, Margaret Sanger met with Dr. Gregory Pincus, a biologist. Pincus had read the current studies on progesterone and believed it was possible to create a drug from it that would prevent ovulation, but he needed funding. Some of the money was provided by Planned Parenthood, while Katherine McCormick, one of Sanger's wealthy supporters, eventually provided more. A progesterone pill had already been created by chemists at two different drug companies, Searle and Syntex, and had already been tested on infertile women by gynecologist John Rock, but neither Sanger nor Pincus were initially aware of this.



Rock and Pincus joined forces in 1954 to conduct the clinical trials required to get FDA funding, with pills provided by Searle. Initially, the pills from Searle were all progesterone. When Rock and Pincus received some pills "contaminated" with estrogen, they discovered that the combination helps to reduce some problems like spotting. In 1956, after further trials in Puerto Rico (done in order to skirt stateside laws against birth control) they concluded that the Searle formulation was the perfect oral contraceptive.

In 1961, the FDA approved the sale of the combination pill, under the name Enovid, by the drug company Searle. Other companies struggled to catch up, and Syntex came out with its own pill under the name Ortho Novum in 1962. A year later, more than 2 million women were on the pill.

Despite its growing popularity, the pill suffered a setback in 1970, when the FDA conducted hearings on its potentially dangerous side effects. Eventually, scientists decided that taking formulations of the pill that contained lower levels of estrogen reduced the incidence of these side effects without reducing the pill's effectiveness. They also concluded that women who smoked while on the pill had the biggest increase in risk. More companies come out with low-dose versions of the pill, and all of the original high-dose versions were taken off the market in 1988.

For more articles you might be interested in, from how Planned Parenthood Works to how a male birth control pill would work, try the links on the next page.

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More Great Links


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