Birth Control Pills - Including effectiveness data and protocols. birth control, the pill, contraceptives, alternatives to condoms An overview of birth control pills, including effectiveness data, societal impact, protocols, and impact on the body. Birth Control Pills

The combined oral contraceptive pill, often referred to as "the Pill", is a combination of an estrogen (oestrogen) and a progestin (progestogen), taken by mouth to inhibit normal fertility. Combined oral contraceptives were first approved for contraceptive use in the United States in 1960, and enjoy great popularity. They are currently used by more than 100 million women worldwide and by almost 12 million women in the United States. Usage varies widely by country, age, education, and marital status: one quarter of women aged 1649 in Great Britain currently use the Pill (combined pill or minipill), but only 1% of women in Japan.


By the 1930s, scientists had isolated and determined the structure of the steroid hormones and found that high doses of androgens, estrogens or progesterone inhibited ovulation, but obtaining them from European pharmaceutical companies produced from animal extracts was extraordinarily expensive.

In 1939, Russell Marker, a professor of organic chemistry at Pennsylvania State University, developed a method of synthesizing progesterone from plant steroid sapogenins, initially using sarsapogenin from sarsaparilla which proved too expensive. After three years of extensive botanical research he discovered a much better starting material, diosgenin from inedible Mexican wild yams found in the jungles of Veracruz near Orizaba. Unable to interest his research sponsor Parke-Davis in the commercial potential of synthesizing progesterone from Mexican yams, Marker left Penn State and in 1944 co-founded Syntex with two partners in Mexico City before leaving Syntex a year later. Syntex broke the monopoly of European pharmaceutical companies on steroid hormones, reducing the price of progesterone almost 200-fold over the next eight years.

In 1940, Percy Lavon Julian's research at Glidden Co.,Chicago,USA took on a new direction when he began work on synthesizing sex steroids: progesterone, estrogen, and testosterone from plant sterols such as stigmasterol, isolated from soybean oil by a "foam" technique he invented. His work made possible the production of these hormones on a large industrial scale, thereby reducing the cost of treating hormonal deficiencies, arthritis, and other disorders and setting the stage for future developments in reproductive research. NOVA - Forgotten Genius -->

Midway through 20th century, the stage was set for the development of a hormonal contraceptive, but pharmaceutical companies, universities and governments showed no interest in pursuing research.

Studies of progesterone to prevent ovulation

In early 1951, reproductive physiologist Gregory Pincus, a leader in hormone research and co-founder of the Worcester Foundation for Experimental Biology (WFEB) in Shrewsbury, Massachusetts, first met American birth control movement founder Margaret Sanger at a Manhattan dinner hosted by Abraham Stone, medical director and vice president of Planned Parenthood (PPFA), who helped Pincus obtain a small grant from PPFA to begin hormonal contraceptive research. Research started on April 25, 1951 with reproductive physiologist Min Chueh Chang repeating and extending the 1937 experiments of Makepeace et al. that showed injections of progesterone suppressed ovulation in rabbits. In October 1951, G. D. Searle & Company refused Pincus' request to fund his hormonal contraceptive research, but retained him as a consultant and continued to provide chemical compounds to evaluate.

In March 1952, Sanger wrote a brief note mentioning Pincus' research to her longtime friend and supporter, suffragist and philanthropist Katharine Dexter McCormick, who visited the WFEB and its co-founder and old friend Hudson Hoagland in June 1952 to learn about contraceptive research there. Frustrated when research stalled from PPFA's lack of interest and meager funding, McCormick arranged a meeting at the WFEB on June 6, 1953 with Sanger and Hoagland where she first met Pincus who committed to dramatically expand and accelerate research with McCormick providing fifty times PPFA's previous funding.

Pincus and McCormick enlisted Harvard clinical professor of gynecology John Rock, chief of gynecology at the Free Hospital for Women and an expert in the treatment of infertility, to lead clinical research with women. At a scientific conference in 1952, Pincus and Rock, who had known each other for many years, discovered they were using similar approaches to achieve opposite goals. In 1952, Rock induced a three-month anovulatory "pseudo-pregnancy" state in eighty of his infertility patients with continuous gradually increasing oral doses of estrogen (diethylstilbestrol 530 mg/day) and progesterone (50300 mg/day) and within the following four months an encouraging 15% became pregnant.

In 1953, at Pincus' suggestion, Rock induced a three-month anovulatory "pseudo-pregnancy" state in twenty-seven of his infertility patients with an oral 300 mg/day progesterone-only regimen for 20 days from cycle days 524 followed by pill-free days to produce withdrawal bleeding. This produced the same encouraging 15% pregnancy rate during the following four months without the troubling amenorrhea of the previous continuous estrogen and progesterone regimen. But 20% of the women experienced breakthrough bleeding and in the first cycle ovulation was suppressed in only 85% of the women, indicating that even higher and more expensive oral doses of progesterone would be needed to initially consistently suppress ovulation.

Studies of progestins to prevent ovulation

Pincus asked his contacts at pharmaceutical companies to send him chemical compounds with progestogenic activity. Chang screened nearly 200 chemical compounds in animals and found the three most promising were Syntex's norethindrone and Searle's norethynodrel and norethandrolone.

Chemists Luis E. Miramontes, Carl Djerassi and George Rosenkranz at Syntex in Mexico City had synthesized the first orally highly active progestin norethindrone in 1951. Chemist Frank B. Colton at Searle in Skokie, Illinois had synthesized the orally highly active progestins norethynodrel (an isomer of norethindrone) in 1952 and norethandrolone in 1953.

In December 1954, Rock began the first studies of the ovulation-suppressing potential of 550 mg doses of the three oral progestins for three months (for 21 days per cycledays 525 followed by pill-free days to produce withdrawal bleeding) in fifty of his infertility patients in Brookline, Massachusetts. 5 mg doses of norethindrone or norethynodrel and all doses of norethandrolone suppressed ovulation but caused breakthrough bleeding, but 10 mg and higher doses of norethindrone or norethynodrel suppressed ovulation without breakthrough bleeding and led to a 14% pregnancy rate in the following five months. Pincus and Rock selected Searle's norethynodrel for the first contraceptive trials in women citing its total lack of androgenicity versus Syntex's norethindrone's very slight androgenicity in animal tests.

Development of an effective combined oral contraceptive

Norethynodrel (and norethindrone) were subsequently discovered to be contaminated with a small percentage of the estrogen mestranol (an intermediate in their synthesis), with the norethynodrel in Rock's 1954-5 study containing 4-7% mestranol. When further purifying norethynodrel to contain less than 1% mestranol led to breakthrough bleeding, it was decided to intentionally incorporate 2.2% mestranol, a percentage that was not associated with breakthrough bleeding, in the first contraceptive trials in women in 1956. The norethynodrel and mestranol combination was given the proprietary name Enovid.

The first contraceptive trial of Enovid led by Edris Rice-Wray began in April 1956 in Ro Piedras, Puerto Rico. A second contraceptive trial of Enovid (and norethindrone) led by Edward T. Tyler began in June 1956 in Los Angeles. On January 23, 1957, Searle held a symposium reviewing gynecologic and contraceptive research on Enovid through 1956 and concluded Enovid's estrogen content could be reduced by 33% to lower the incidence of estrogenic gastrointestinal side effects without significantly increasing the incidence of breakthrough bleeding.

Public availability

In June 1957, the FDA approved Enovid 10 mg (9.85 mg norethynodrel and 150 g mestranol) for menstrual disorders based on data from its use by more than 600 women. Numerous additional contraceptive trials showed Enovid at 10, 5, and 2.5 mg doses to be highly effective. On July 23, 1959, Searle filed a supplemental application to add contraception as an approved indication for 10, 5 and 2.5 mg doses of Enovid. The FDA refused to consider the application until Searle agreed to withdraw the lower dosage forms from the application. On May 9, 1960, the FDA announced it would approve Enovid 10 mg for contraceptive use, which it did on June 23, 1960, by which time Enovid 10 mg had been in general use for three years during which time, by conservative estimate, at least half a million women had used it.

Although FDA-approved for contraceptive use, Searle never marketed Enovid 10 mg as a contraceptive. Nine months later, in February 1961, the FDA approved Enovid 5 mg for contraceptive use. In July 1961, Searle finally began marketing Enovid 5 mg (5 mg norethynodrel and 75 g mestranol) to physicians as a contraceptive.

Although the FDA approved the first oral contraceptive in 1960, contraceptives were not available to married women in all states until Griswold v. Connecticut in 1965 and were not available to unmarried women in all states until Eisenstadt v. Baird in 1972.

The first published case report of a blood clot and pulmonary embolism in a woman using Enovid did not appear until November 1961, four years after its approval, by which time it had been used by over one million women. It would take almost a decade of epidemiological studies to conclusively establish an increased risk of venous thrombosis in oral contraceptive users and an increased risk of stroke and myocardial infarction in oral contraceptive users who smoke or have high blood pressure or other cardiovascular or cerebrovascular risk factors. These risks of oral contraceptives were dramatized in the 1969 book The Doctors' Case Against the Pill by feminist journalist Barbara Seaman who helped arrange the 1970 Senate hearings called by Senator Gaylord Nelson. The hearings were conducted by Senators who were all men and the witnesses in the first round of hearings were all men, leading Alice Wolfson and other feminists to protest the hearings and generate media attention. Their work led to mandating the inclusion of patient package inserts with oral contraceptives to explain their possible side effects and risks to help facilitate informed consent. Today's standard dose oral contraceptives contain an estrogen dose that is one third lower than the first marketed oral contraceptive and contain lower doses of different, more potent progestins in a variety of formulations.


In 1967, the Neuwirth Law legalized contraception in France, including the pill. The pill is the most popular form of contraception in France, especially among young women. The abortion rate has remained stable since the introduction of the pill.


In Japan, lobbying from the Japan Medical Association prevented the Pill from being approved for nearly 40 years. Two main objections raised by the association were safety concerns over long-term use of the Pill, and concerns that the Pill use would lead to diminished use of condoms and thereby potentially increase sexually transmitted infection (STIs) rates. As of 2004, condoms accounted for 80% of birth control use in Japan, and this may explain Japan's comparably low rates of AIDS.

The Pill was approved for use in 1999; the Pill prescription guidelines the government endorsed require Pill users to visit

a doctor every three months for pelvic examinations and undergo tests for sexually transmitted diseases and uterine cancer. In the United States and Europe, in contrast, an annual or bi-annual clinic visit is standard for Pill users.

Use and Packaging

Combined oral contraceptive pills must be ingested at the same time each day. Women must take the pill within a two hour window each day to ensure its effectiveness. Most brands of combined pills are packaged in one of two different packet sizes, with days marked off for a 28 day cycle. For the 21-pill packet, a pill is consumed daily for three weeks, followed by a week of no pills. For the 28-pill packet, 21 pills are taken, followed by week of placebo or sugar pills. A woman on the pill will have a withdrawal bleed sometime during the placebo week.

Placebo pills

The purpose of the placebo pills is that the user, out of habit, can take a pill on every day of her menstrual cycle, instead of calculating the date she should start the next dose. Placebo pills may contain an iron supplement, as iron requirements increase during menstruation.

Failure to take pills during the placebo week has no effect on the effectiveness of the pill provided that daily ingestion of active pills is resumed at the end of the week.

The presence of placebo pills is thought to be comforting, as menstruation is a physical confirmation of not being pregnant. The 28-day pill package also simulates the average menstrual cycle, though the hormonal events during a pill cycle are completely different from those of a normal ovulatory menstrual cycle, and the bleeding is triggered by different homonal cues. Breakthrough bleeding also becomes a more common side effect as a woman attempts to go longer periods of time between menstrual periods.

Less frequent placebos

If the pill formulation is monophasic, it is possible to skip menstruation and still remain protected against conception by skipping the placebo pills and starting directly with the next packet. Attempting this with bi- or tri-phasic pill formulations carries an increased risk of breakthrough bleeding and may be undesirable. It will not, however, increase the risk of getting pregnant.

Starting in 2003, women have also been able to use a three-month version of the Pill. Similar to the effect of using a constant-dosage formulation and skipping the placebo weeks for three months, Seasonale gives the benefit of less frequent periods, at the potential drawback of breakthrough bleeding. Seasonique is another version in which the placebo week every three months is replaced with a week of low-dose estrogen.

A version of the combined pill has also been packaged to completely eliminate placebo pills and withdrawal bleeds. Marketed as Anya or Lybrel, studies have shown that after seven months 71% of users no longer had any breakthrough bleeding, the most common side effect of going longer periods of time without breaks from active pills.


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

If a woman just starting the pill begins taking them within five days of the beginning of her menstrual cycle (the menstrual cycle begins on the first day of red bleeding), she will have pregnancy protection from the very first pill. If a woman begins taking the pill at another time in her menstrual cycle, she must use a different form of contraception for seven days.

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 can also stop the Pill from working, because it causes the hormones to not be properly absorbed by the bowels.

Mechanism of action

Prefertilization effects

The combined Pill primarily prevents pregnancy by preventing ovulation. In women who take the pills correctly, ovulation is prevented in 98-99% of cycles. Forgetting to take one or more pills increases ovulation rates; one study found skipping two pills in a row resulted in ovulation in 29% of cycles. (In women not taking the Pill, pregnancy occurs in approximately 25% of ovulatory cycles.)

In the event of breakthrough ovulation, secondary contraceptive mechanisms are believed to come into play. A proposed secondary mechanism prior to fertilization (creation of the embryo) is creation of an environment hostile to the embryo's implantation and survival. Proposed secondary mechanisms active before fertilization include thickening of cervical mucus, which can prevent or slow sperm entry into the uterus, and changes in tube transport inhibiting sperm migration to the fallopian tubes.

Postfertilization effects

Postfertilization effects of combined oral contraceptives (COCs) could involve any 1 or more of the following 3 mechanisms of action:

Thinning and other changes to the endometrium are well-documented. Experience with in vitro fertilization has shown that similar changes are detrimental to implantation rates. However, some physicians are unconvinced that these pill-induced changes truly decrease the likelihood that an embryo will implant itself in the uterine lining. In women who do not take the Pill, the uterine lining is usually unreceptive to implantation prior to ovulation. The purpose of the hormones released by the corpus luteum is to cause the endometrium to thicken and become receptive to implantation (which occurs between six and twelve days after ovulation if the ovum is fertilized). Thus, simple observations that the uterine lining is too thin to support implantation during a cycle where no ovulation has occurred is insufficient to support the claim that there is a reduced likelihood of implantation in ovulatory Pill cycles. Currently, very little research has been conducted on the behavior of the endometrium in ovulatory Pill cycles. Others point to studies showing reduced volume of menstrual flow for several cycles after discontinuing use of COCs, suggesting that the endometrium is slow to recover from its COC-induced atrophy. They also present studies demonstrating luteal phase defect in ovulatory pill cycles. These two effects would support the existance of a postfertilization mechanism of action.

The theoretical increased rate of miscarriage among post-implantation but pre-clinically recognized pregnancies could be tested with serial ultrasensitive assays for human chorionic gonadotropin. To date, no such trials have been conducted in women taking combined oral contraceptive pills.

The theory that the pill has a postfertilization effect due to slowed tube transport holds that the ratio of extrauterine to intrauterine pregnancies is increased in women using the pill. Supporting this theory, one study found that women who became pregnant while taking the combined pill were 13.9 times more likely to have an ectopic pregnancy than women who became pregnant while not using a contraceptive method (only pregnancies that were ectopic or ended in live birth were included in this study; not including pregnancies that ended in abortion possibly introduced error into the ratio calculation). A study by the World Health Organization found no such increased risk.

Drug interactions

Some drugs reduce the effect of the Pill and can cause breakthrough bleeding, or increased chance of pregnancy. These include enzyme inducing drugs such as rifampicin, barbiturates, phenytoin and carbamazepine. In addition cautions are given about broad spectrum antibiotics, such as ampicillin and doxycycline, which may cause problems "by impairing the bacterial flora responsible for recycling ethinylestradiol from the large bowel" (BNF 2003).

The traditional medicinal herb St John's Wort has also been implicated due to its upregulation of the P450 system in the liver.


When starting to take the Pill, the majority (about 60%) of women report no side effects at all, and the vast majority of those who do, have only minor effects. A 1992 French review article said that as many as 50% of new Pill users discontinue use before the end of the first year because of side effects.

The same 1992 French review article noted that one study found that 20-25% of women reported they stopped taking the Pill because of either acne or weight gain. A 1986 Hungarian study comparing two high-dose estrogen (both 50 g ethinyl estradiol) pills found that women using a lower-dose biphasic levonorgestrel formulation (50 g levonorgestrel x 10 days + 125 g levonorgestrel x 11 days) reported a significantly lower incidence of weight gain compared to women using a higher-dose monophasic levonorgestrel formulation (250 g levonorgestrel x 21 days). Many clinicians consider the public percerption of weight gain on the Pill to be inaccurate and dangerous. The aforementioned 1992 French review article noted that one study of 550 women found that 23% of the 6% of women who discontinued the Pill because of poor cycle control experienced subsequent unwanted pregnancies. A 2000 British review article concluded there is no evidence that modern low-dose pills cause weight gain, but that fear of weight gain contributed to poor compliance in taking the Pill and subsequent unintended pregnancy, especially among adolescents.

Other possible side effects are: changes in the intensity of sexual desire, vaginal discharge, changes in menstrual flow, breakthrough bleeding, unusual build-up of the uterine lining, nausea, headaches, depression, vaginitis, urinary tract infection, changes in the breasts, changes in blood pressure, skin problems, skin improvements, and gum inflammation. The insert included with each pill packet usually has a more extensive list of recognized side effects.

Effects on Sexuality

Some say the Pill may have a positive effect on a woman's sexuality. Because neither the woman (who uses the Pill) nor her partner need take any special action before or during intercourse, it makes birth control "invisible" and sex spontaneous, more natural, or both. When combined with the Pills high degree of effectiveness, this may enable the couple, and especially the woman, to relax more easily during sex. Masters and Johnson reported more than one woman who experienced her first orgasm during intercourse shortly after going on the Pill.

However, some say the Pill can also have a negative effect on a woman's sexuality. Dr. John Bancroft (a senior research fellow at the Kinsey Institute at Indiana University) estimates that one in four women on the pill experience some negative sexual effect. These effects may include a decreased frequency of sexual thoughts, increased difficulty in becoming aroused, or decreased lubrication, which can make sex painful. Recent research co-authored by Dr. Irwin Goldstein (a urologist in Boston) suggests such effects may continue for up to four months after a woman stops taking the Pill.

Emotional side effects

Studies and anecdotal sources have also demonstrated that the ingestion of birth control pills can cause, quite often, negative emotional side effects on women, including depression, mood swings, and anxiety.

While researchers have noted the importance of discovering what causes these side effects, there is no clear understanding as to why this happens.


Oral contraceptives come in a variety of formulations. The main division is between combined oral contraceptive pills, containing both estrogen and progestins and progestin only pills. Combined oral contraceptive pills also come in varying types, including varying doses of estrogen, and whether the dose of estrogen or progestin changes from week to week.

Cautions and contraindications

Oral contraceptives may influence coagulation, subtly increasing the risk of deep venous thrombosis (DVT) and pulmonary embolism, stroke and myocardial infarction (heart attack). However, estrogen contraceptives are usually only contraindicated in women with pre-existing cardiovascular disease, in women who have a familial tendency to form blood clots (such as familial factor V Leiden), women with severe obesity and/or hypercholesterolaemia (high cholesterol level) and most notably in smokers over 35.

Studies of higher-dose, estrogen-based pills have been linked to an increased risk of breast cancer, though no studies have been done on the lower-dose pills more popular today. In rare cases, high estrogen Pills may trigger benign intracranial hypertension.

Research into the risk of breast cancer and hormonal contraception is complex and contradictory. There "is a small increase in the risk of having breast cancer diagnosed in current users of combined oral contraceptives and in women who had stopped use in past 10 years but there is no evidence of an increase in the risk more than 10 years after stopping use" and the nature of the identified cancers being less advanced clinically suggested a bias of screening in oral contraceptives users.

More recently, the Mayo Clinic Proceedings published a meta-analysis in October 2006 by the founder and president of TRPI (The Polycarp Research Institute - that "will not promote methods or intentions that are inconsistent with the ethical and moral guidelines of the Catholic Church") revealing that 21 of 23 studies that followed women who took oral birth control before having their first child showed an increased risk of early breast cancer.

In Our Sexuality, Crooks and Baur state a commonly held medical opinion about risks associated with Pill use: "In general, the health risks of oral contraceptives are far lower than those from pregnancy and birth." Although widely accepted, at least one organization disputes that conclusion, and others have argued that comparing a contraceptive method to no method (pregnancy) is not relevant - instead, the comparison of safety should be among available methods of contraception.

Non-contraceptive uses

The hormones in "the Pill" can be used to treat some medical conditions, such as polycystic ovary syndrome (PCOS), endometriosis, adenomyosis, anemia related to menstruation, and painful menstruation (dysmenorrhea). In addition, oral contraceptives are often prescribed as medication for mild or moderate acne. The pill can also induce bleeding on a regular schedule for women bothered by irregular menstrual cycles and certain disorders where there is dysfunctional uterine bleeding.

Combined oral contraceptive use reduces the risk of ovarian cancer by 40% and the risk of endometrial cancer by 50% compared to never users. The risk reduction increases with duration of use, with an 80% reduction in risk for both ovarian and endometrial cancer with use for more than 10 years. The risk reduction for both ovarian and endometrial cancer persists for at least 20 years.

Although the FDA does not officially condone the use of the Pill as a minor breast enhancer, many women have gone on the pill in order to increase their breast size. This results from the low doses of estrogen present along with the progestin. Results vary widely.

Social and cultural impact

Introduced at the beginning of the tumultuous decade of the 1960s, the Pill had a big social impact. In the first place, it was far more effective than any previous method of birth control, giving women unprecedented control over their fertility. Its use was separate from intercourse, requiring no special preparations at the time of sexual activity that might interfere with spontaneity or sensation. This combination of factors served to make the Pill immensely popular within a few years of its introduction.

Because the Pill was so effective, and soon so widespread, it also heightened the debate about the moral and health consequences of pre-marital sex and promiscuity. Never before had sexual activity been so divorced from reproduction. For a couple using the Pill, intercourse became purely an expression of love, or a means of physical pleasure, or both; but it was no longer a means of reproduction. While this was true of previous contraceptives, their relatively high failure rates and their less widespread use failed to emphasize this distinction as clearly as did the Pill. The spread of oral contraceptive use thus led many religious figures and institutions to debate the proper role of sexuality and its relationship to procreation. The Roman Catholic Church in particular, after studying the phenomenon of oral contraceptives, re-emphasized traditional Catholic teaching on birth control in the 1968 papal encyclical Humanae Vitae. The encyclical, reiterated the traditional Catholic teaching that artificial contraception distorted the nature and purpose of sex.

A backlash against oral contraceptives occurred in the early and mid-1970s, when reports and speculations appeared that linked the use of the Pill to breast cancer. Until then, many women in the feminist movement had hailed the Pill as an "equalizer" that had given them the same sexual freedom as men had traditionally enjoyed. This new development, however, caused many of them to denounce oral contraceptives as a male invention designed to facilitate male sexual freedom with women at the cost of health risk to women. At the same time, society was beginning to take note of the impact of the Pill on traditional gender roles. Women now did not have to choose between a relationship and a career; singer Loretta Lynn commented on this in her 1974 album with a song entitled "The Pill," which told the story of a married woman's use of the drug to liberate herself from her traditional role as wife and mother.

Environmental impact

Ethinylestradiol, the synthetic estrogen used in most combined hormonal contraceptives, is excreted in the urine of women users. Sewage treatment processes do not remove these chemicals, and they are discharged into the water system. This form of pollution has been proven to have reproductive and other effects on aquatic organisms, including fish, frogs, and zooplankton. Feminization of male fish, even to the point of producing eggs, is one common effect. Both male and female fish experience delays in reproductive development, and changes are seen in their kidneys and livers.

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