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Oral contraceptive

Oral contraceptives are chemicals taken by mouth to inhibit normal fertility. All act on the hormonal system. Female oral contraceptives have been on the market since the early 1960s, and enjoy great popularity. They are used by millions of women around the world, though the acceptance varies by region: approximately one-third of sexually active women in the United Kingdom, but much less in countries such as Japan. Male oral contraceptives remain a subject of research and development, and are not widely available to the public.


Female oral contraceptives, colloquially known as the Pill, are the most common form of pharmaceutical contraception. They are used to prevent pregnancy. The pill can also be used to control dysfunctional bleeding or symptoms of polycystic ovary syndrome. They consist of a pill that women take daily and that contains doses of synthetic hormones (always a progestin and most often also an estrogen). In some types of pill the doses of hormones are adjusted to be in synchrony with the menstrual cycle (two- or three-phase pills), while others keep a constant level of the hormones.

Mechanism of action

The Pill prevents pregnancy in three ways. It works primarily by preventing ovulation, but it also makes the uterus less likely to accept implantation of an embryo if one is created. The synthetic hormones thicken the mucus in the cervix making it more difficult for sperm to reach any egg.

Several different types of 'the Pill' exist. Generally, they all have different synthetic estrogens and progestins, chemical analogues of the natural hormones: estradiol (an estrogen) and progesterone (a progestagen). Most common brands use 20 to 40 micrograms of ethinyl estradiol as the estrogen component and either a fixed or varying (the bi- and triphasic pills) amount of either levonorgestrel or norethindrone as the progestagen component.

Please see Progesterone only pills which, lacking any estrogen, have much less of the side-effects and complications that apply to combined pills.


The Pearl Index[1] is often used to compare the effectiveness of various methods of contraception. It is expressed as the "number of pregnancies in 100 normally fertile women over the period of one year". Each method of birth control has two Pearl index numbers:

  • method effectiveness: is the Pearl index number for use under perfect conditions. The method effectiveness Pearl index for the Pill has been measured as low as 0.3 and as high as 1.25, which means that under ideal conditions, anywhere from 0.3 to 1.25 out of 100 users will become pregnant during one year of perfect use (Pearl index = 0.3 to 1.25).
  • user effectiveness: is the Pearl index number for use under typical conditions. The user effectiveness measured by the Pearl index for the Pill has been measured as low as 2.15 and as high as 8.0, which means that anywhere from 2.15 to 8.0 out of 100 women will become pregnant during the first year of typical use (Pearl index = 2.15 to 8.0). [2] [3]

Many women occasionally forget to take the Pill daily, impairing its effectiveness. Correct use of the pill usually implies taking it every day at the same hour for 21 days, followed by a pause of seven days.

Use of other medications can prevent the Pill from working, due to interactions with the metabolism of the hormonal constituents. Diarrhea will also stop the Pill from working, because the hormones are not properly absorbed by the bowels.

While the Pill is usually effective, its wide availability has not prevented unplanned pregnancies. In the USA, the rise in widespread use of the Pill has coincided with a rise in the abortion rate to a level that is consistently above 1,000,000 per year, according to AGI statistics.


Half-used blister pack of Levlen®ED
Half-used blister pack of Levlen®ED

The Pill usually comes in two different packet sizes, and each packet usually has days marked off for a cycle lasting of 28 days. For the 21-pill packet, a woman takes a pill each day for 21 days, and waits for an additional seven days before starting the next packet. For the 28-pill packet, the woman similarly takes a pill each day. However, instead of only taking pills for 21 days of the month, she also takes the remaining seven placebo or sugar pills included in the packet, and once she finishes the last placebo pill, she can immediately start the next packet on the following day. The purpose of the placebo pills is to ensure that the woman, out of habit, can take a pill on every day of her menstrual cycle, so that she does not have to calculate when exactly is the next date that she should start her next packet of pills. It is possible for a woman to skip menstruation and still remain protected against conception by skipping these pills in the cycle. The presence of these pills is still thought to be comforting for the woman as menstruation is a physical confirmation that she is still not pregnant.

Drug interactions

Some drugs reduce the effect of the Pill and can cause breakthrough bleeding, or pregnancy (together with unprotected sex, of course). These include antibiotics, barbiturates, phenytoin and carbamazepine. The traditional medicinal herb St John's Wort has also been implicated.


When starting to take the Pill some women report slight weight gain, although this depends entirely on the individual and some people experience no weight gain at all while people who are already obese or overweight may continue to gain weight. Some people also notice changes in the intensity of sexual desire, vaginal discharge and menstrual flow.

Some other common side effects are: nausea, headaches, depression, vaginitis, urinary tract infection, changes in the breasts, changes in blood pressure, skin problems, skin improvements, and gum inflammation.


See oral contraceptive formulations

Effects on sexuality

The effect of the Pill on a woman’s sexuality are difficult to judge; depending on the individual and the particular formula, the Pill may enhance or disrupt a woman’s (or couple’s) sex life. Neither the woman who uses the Pill nor her partner need take any special action before or during intercourse, which makes birth control “invisible” and sex spontaneous and more natural. When combined with the Pill’s high degree of effectiveness, this may enable the couple, and especially the woman, to relax more easily during sex. Masters and Johnson, among others, reported more than one woman who experienced her first orgasm during intercourse shortly after going on the Pill.

On the other hand, the Pill’s various side effects may prove disruptive on a physiological or even a psychological level. The hormonal disruption caused by the Pill may result in mood swings, lower libido, excessive or insufficient vaginal lubrication during intercourse, and possibly an injured self-image due to weight gain. Some women who use the Pill despite the teachings of their religious traditions may feel conscious or unconscious guilt; others may not fully trust an “invisible” method of birth control. This wide range of variables makes prediction of the Pill’s effect on sexuality difficult, but the fact that the Pill can and does have an impact in this area, for good or for ill, is well-documented.

Cautions and contraindications

Oral contraceptives may influence coagulation, increasing the risk of blood clots causing deep venous thrombosis (DVT) and pulmonary embolism, stroke and myocardial infarction (heart attack). This is especially so in women who already have some pre-existing cardiovascular disease, in women who have a familial tendency to form blood clots (such as familial factor V Leiden), women with obesity or hypercholesterolaemia (high cholesterol level) and in smokers.

The Pill has also been linked to an increased risk of breast cancer, although newer Pill types may not influence breast cancer risk. In rare cases, high estrogen Pills may trigger benign intracranial hypertension. Women who use the Pill have an increased chance of developing certain serious problems that can be fatal. Benign liver tumors have been reported.

The chance of developing most of the above problems increases with age - especially when certain other health problems are present. The risks are even greater for women who are age 35 or older, smoke more than 15 cigarettes a day, or have conditions associated with heart attack, such as diabetes, high blood pressure, or high levels of cholesterol, and certain inherited conditions that increase the risk of blood clotting. Women using the Pill who undergo major surgery seem to have a greater chance of having blood clots.


Aside from being a contraceptive and for management of irregular periods, there may be incidental benefits to the Pill. There is some evidence that use of the pill might reduce the incidence of ovarian cancer and endometrial cancer [4]. Given that the benefits are less well researched or highlighted than the risks, the question arises as to how the reduction in incidence of these cancers compares against the increased risks of developing breast cancer or deep-vein thrombosis.


The invention

The Pill was developed in the 1950s by Gregory Pincus with the encouragement and financial backing of birth control activists Margaret Sanger and Katharine McCormick. Carl Djerassi (1923-) invented norethindrone in the 1950s. This creation provided a large enough supply of synthetic hormone to produce "the pill" for mass markets.

The FDA approved it for clinical use on May 9, 1960. It took various high-profile court cases, such as Poe v. Ullman and Griswold v. Connecticut, to make it available to all women of reproductive age.


The Pill was rendered legal in 1967 after the introduction of the Neuwirth Law.


In Japan, continual debates over safety and sexually-transmitted infection risks (raised over concerns that oral contraceptive use will diminish condom use) have led to the Pill being banned for nearly 40 years, and its recent introduction has seen very few women take it up[5].


  1. ^  Pearl R. Factors in human fertility and their statistical evaluation. Lancet 1933;2:607-611.
  2. ^  Data based on article: Audet MC, Moreau M, Koltun WD, Waldbaum AS, Shangold G, Fisher AC, Creasy GW. Evaluation of contraceptive efficacy and cycle control of a transdermal contraceptive patch vs an oral contraceptive: a randomized controlled trial. JAMA. 2001;285(18):2347-2354. (http://www.contraceptiononline.org/slides/slide01.cfm?q=pearl+index&dpg=6)
  3. ^  Alan Guttmacher Institute, Facts in Brief, First Year Contraceptive Failure Rates (http://www.agi-usa.org/pubs/fb_contr_use.html). Retrieved May 10, 2005.
  4. ^  Reduction in ovarian & endometrial cancer study. http://content.nejm.org/cgi/content/abstract/316/11/650
  5. ^  Hormonal contraceptive use in Japan, 2004 news article. (http://www.cbsnews.com/stories/2004/08/20/health/main637523.shtml)

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