出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/06/07 13:54:56」(JST)
| Combined oral contraceptive pill (COCP) | |
|---|---|
| Background | |
| Birth control type | Hormonal |
| First use | 1960 USA |
| Failure rates (first year) | |
| Perfect use | 0.3[1]% |
| Typical use | 9[1]% |
| Usage | |
| Duration effect | 1–4 days |
| Reversibility | Yes |
| User reminders | Taken within same 24-hour window each day |
| Clinic review | 6 months |
| Advantages and disadvantages | |
| STD protection | No |
| Periods | Regulates, and often lighter and less painful |
| Weight | No proven effect |
| Benefits | Reduced mortality risk.[2] Reduced death rates in all cancers.[2] Reduced ovarian and endometrial cancer risks. May treat acne, PCOS, PMDD, endometriosis |
| Risks | Possible small increase in some cancers.[3][4] Small reversible increase in DVTs; Stroke,[5] Cardio-vascular disease[6] |
| Medical notes | |
| Affected by the antibiotic rifampin,[7] the herb Hypericum (St. Johns Wort) and some anti-epileptics, also vomiting or diarrhea. Caution if history of migraines. | |
The combined oral contraceptive pill (COCP), often referred to as the birth-control pill or colloquially as "the pill", is a birth control method that includes a combination of an estrogen (estradiol) and a progestogen (progestin). When taken by mouth every day, these pills inhibit female fertility. They were first approved for contraceptive use in the United States in 1960, and are a very popular form of birth control. They are currently used by more than 100 million women worldwide and by almost 12 million women in the United States.[8] Use varies widely by country,[9] age, education, and marital status: one third of women[10] aged 16–49 in the United Kingdom currently use either the combined pill or a progestogen-only "minipill",[11] compared to only 1% of women in Japan.[12]
Combined oral contraceptive pills should be taken at the same time each day. If one or more tablets are forgotten for more than 12 hours, contraceptive protection will be reduced.[13] 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, and is still protected from pregnancy during this week. There are also two newer combination birth control pills (Yaz 28 and Loestrin 24 Fe) that have 24 days of active hormone pills, followed by 4 days of placebo.[14]
The placebo pills allow the user to take a pill every day; remaining in the daily habit even during the week without hormones. Placebo pills may contain an iron supplement,[15][16] as iron requirements increase during menstruation.
Failure to take pills during the placebo week does not impact the effectiveness of the pill, provided that daily ingestion of active pills is resumed at the end of the week.
The withdrawal bleeding that occurs during the break from active pills was thought to be comforting, as a physical confirmation of not being pregnant.[17] The 28-day pill package also simulates the average menstrual cycle, though the hormonal events during a pill cycle are significantly different from those of a normal ovulatory menstrual cycle. The pill suppresses the normal cycle, and the withdrawal bleeding occurs while the placebo pills are taken. The withdrawal bleeding is also predictable. Unexpected breakthrough bleeding can be a possible side effect of longer term active regimens.[18]
If the pill formulation is monophasic, it is possible to skip withdrawal bleeding 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.[19] 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.[20]
According to James Trussell's Contraceptive Efficacy chapter in the current (2011) edition of Contraceptive Technology, the estimated probability of pregnancy during the first year of perfect use of pill is 0.3%, and the estimated probability of pregnancy during the first year of typical use of the pill is 9%.[1] The perfect use failure rate is based on a review of pregnancy rates in clinical trials of the pill, the typical use failure rate is based on a weighted average of estimates from the 1995 and 2002 U.S. National Surveys of Family Growth (NSFG) conducted by the National Center for Health Statistics (NCHS), corrected for underreporting of abortions.[1]
Several factors account for typical use effectiveness being lower than perfect use effectiveness:
For instance, someone using oral forms of hormonal birth control might be given incorrect information by a health care provider as to the frequency of intake, or by mistake not take the pill one day, or simply not go to the pharmacy on time to renew the prescription.
COCPs provide effective contraception from the very first pill if started within five days of the beginning of the menstrual cycle (within five days of the first day of menstruation). If started at any other time in the menstrual cycle, COCPs provide effective contraception only after 7 consecutive days use of active pills, so a backup method of contraception must be used until active pills have been taken for 7 consecutive days. COCPs should be taken at approximately the same time every day.[21][22]
Contraceptive efficacy may be impaired by: 1) missing more than one active pill in a packet, 2) delay in starting the next packet of active pills (i.e., extending the pill-free, inactive or placebo pill period beyond 7 days), 3) intestinal malabsorption of active pills due to vomiting or diarrhea, 4) drug interactions with active pills that decrease contraceptive estrogen or progestogen levels.[21]
The hormones in "the Pill" have also been used to treat other medical conditions, such as polycystic ovary syndrome (PCOS), endometriosis, amenorrhea, menstrual cramps, adenomyosis, menorrhagia (excessive menstral bleeding), menstruation-related anemia and dysmenorrhea (painful menstruation).[23] Though extensively used for these conditions, no oral contraceptives have been approved by the U.S. FDA for those uses because of lack of convincing scientific evidence that the benefits outweigh the risks.[citation needed] In addition, oral contraceptives are sometimes prescribed as medication for mild or moderate acne, although none are approved by the U.S. FDA for that sole purpose.[24] Three different oral contraceptives have been FDA approved to treat moderate acne if the person is at least 14 or 15 years old, have already begun menstruating, and need contraception. They include Ortho Tri-Cyclen, Estrostep, and YAZ.[25] Although the pill is sometimes prescribed to induce menstruation on a regular schedule for women bothered by irregular menstrual cycles, it actually suppresses the normal menstrual cycle and then mimics a regular 28-day monthly cycle, as noted earlier in this article.
Some drugs reduce the effect of the Pill and can cause breakthrough bleeding, or increased chance of pregnancy. These include 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).[26][27][28][29]
The traditional medicinal herb St John's Wort has also been implicated due to its upregulation of the P450 system in the liver.
Different sources note different incidences of side effects. The most common side effect is breakthrough bleeding. A 1992 French review article said that as many as 50% of new first-time users discontinue the birth control pill before the end of the first year because of the annoyance of side effects such as breakthrough bleeding and amenorrhea.[30] One study found that women using birth control pills blinked 32% more often than those not using the contraception.[31]
On the other hand, the pills can sometimes improve conditions such as pelvic inflammatory disease, dysmenorrhea, premenstrual syndrome, and acne,[32] reduce symptoms of endometriosis and polycystic ovary syndrome, and decrease the risk of anemia.[33] Use of oral contraceptives also reduces lifetime risk of ovarian cancer.[34][35]
Nausea, vomiting, headache, bloating, breast tenderness, swelling of the ankles/feet (fluid retention), or weight change may occur. Vaginal bleeding between periods (spotting) or missed/irregular periods may occur, especially during the first few months of use.[36]
It is generally accepted by medical authorities that the health risks of oral contraceptives are lower than those from pregnancy and birth,[37] and "the health benefits of any method of contraception are far greater than any risks from the method".[38] Some organizations 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.[39]
Combined oral contraceptives increase the risk of venous thromboembolism (including deep vein thrombosis [DVT] and pulmonary embolism [PE]).[40] These blood clots can cause permanent disability or death. COC pills also confer a risk of first ischemic stroke,[5] and current use significantly increases the risk of cardio-vascular disease among those at high risk.[6] These risks are greatest in women with additional risk factors, such as smoking (which increases risk substantially) and long-continued use of the pill, especially in women over 35 years of age.[41]
The overall absolute risk of venous thrombosis per 100.000 woman years in current use of combined oral contraceptives is approximately 60, compared to 30 in non-users.[42] The risk of thromboembolism varies with different types of birth control pills; compared with combined oral contraceptives containing levonorgestrel (LNG), and with the same dose of estrogen and duration of use, the rate ratio of deep venous thrombosis for combined oral contraceptives with norethisterone is 0.98, with norgestimate 1.19, with desogestrel (DSG) 1.82, with gestodene 1.86, with drospirenone (DRSP) 1.64, and with cyproterone 1.88.[42] In comparison, venous thromboembolism occurs in 100–200 per 100.000 pregnant women every year.[42]
One study showed more than a 600% increased risk of blood clots for women taking COCPs with drospirenone compared to non-users, compared to 360% higher for women taking birth control pills containing levonorgestrel.[43] The U.S. Food and Drug Administration (FDA) initiated studies evaluating the health of more than 800,000 women taking COCPs and found that the risk of VTE was 93% higher for women who had been taking drospirenone COCPs for 3 months or less and 290% higher for women taking drospirenone COCPs for 7–12 months, compared to women taking other types of oral contraceptives.[44]
Based on these studies, in 2012 the FDA updated the label for drospirenone COCPs to include a warning that contraceptives with drospirenone may have a higher risk of dangerous blood clots.[45]
A systematic review in 2010 did not support an increased overall cancer risk in users of combined oral contraceptive pills, but did find a slight increase in breast cancer risk among current users, which disappears 5–10 years after use has stopped.[46]
COC decrease the risk of ovarian cancer, endometrial cancer,[21] and colorectal cancer.[3][32][47] Two large cohort studies published in 2010 both found a significant reduction in adjusted relative risk of ovarian and endometrial cancer mortality in ever-users of OCs compared to never-users.[2][48]
The use of oral contraceptives (birth control pills) for five years or more decreases the risk of ovarian cancer in later life by 50%.[47] 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.[21]
A report by a 2005 International Agency for Research on Cancer (IARC) working group said COCs increase the risk of cancers of the breast (among current and recent users),[3] cervix and liver (among populations at low risk of hepatitis B virus infection).[3] Two large cohort studies published in 2010 both found no significant increase in adjusted relative risk of breast cancer mortality in ever-users of OCs compared to never-users.[2][48]
Research into the relationship between breast cancer risk and hormonal contraception is complex and seemingly contradictory.[49] A large 1996 collaborative reanalysis of individual data on over 150,000 women in 54 studies of breast cancer found that: "The results provide strong evidence for two main conclusions. First, while women are taking combined oral contraceptives and in the 10 years after stopping there is a small increase in the relative risk of having breast cancer diagnosed. Second, there is no significant excess risk of having breast cancer diagnosed 10 or more years after stopping use. The cancers diagnosed in women who had used combined oral contraceptives were less advanced clinically than those diagnosed in women who had never used these contraceptives."[4] These data suggest that oral contraceptives have little effect on breast cancer development, or that women who seek gynecologic care to obtain contraceptives have more early breast cancers detected through screening.[50][51]
A 2011 Cochrane systematic review found that studies of combination hormonal contraceptives showed no large difference in weight when compared with placebo or no intervention groups.[52] The evidence was not strong enough to be certain that contraceptive methods do not cause some weight change, but no major effect was found.[52] This review also found "that women did not stop using the pill or patch because of weight change."[52]
COCPs may increase natural vaginal lubrication.[53] Other women experience reductions in libido while on the pill, or decreased lubrication.[53][54] Some researchers question a causal link between COCP use and decreased libido;[55] a 2007 study of 1700 women found COCP users experienced no change in sexual satisfaction.[56] A 2005 laboratory study of genital arousal tested fourteen women before and after they began taking COCPs. The study found that women experienced a significantly wider range of arousal responses after beginning pill use; decreases and increases in measures of arousal were equally common.[57]
A 2006 study of 124 pre-menopausal women measured sex hormone binding globulin (SHBG), including before and after discontinuation of the oral contraceptive pill. Women continuing use of oral contraceptives had SHBG levels four times higher than those who never used it, and levels remained elevated even in the group that had discontinued its use.[58] Theoretically, an increase in SHBG may be a physiologic response to increased hormone levels, but may decrease the free levels of other hormones, such as androgens, because of the unspecificity of its sex hormone binding.
Low levels of serotonin, a neurotransmitter in the brain, have been linked to depression. High levels of estrogen, as in first-generation COCPs, and progestin, as in some progestin-only contraceptives, have been shown to promote the lowering of brain serotonin levels by increasing the concentration of a brain enzyme that reduces serotonin. This observation, along with some small research studies[59] have inspired speculation that the pill causes depression.
Progestin-only contraceptives are known to worsen the condition of women who are already depressed.[60] However, current medical reference textbooks on contraception[21] and major organizations such as the American ACOG,[61] the WHO,[62] and the United Kingdom's RCOG[63] agree that current evidence indicates low-dose combined oral contraceptives are unlikely to increase the risk of depression, and unlikely to worsen the condition in women that are currently depressed. Contraceptive Technology states that low-dose COCPs have not been implicated in disruptions of serotonin or tryptophan. However, some studies provide evidence to contradict this last claim.[64]
Bradykinin lowers blood pressure by causing blood vessel dilation. Certain enzymes are capable of breaking down bradykinin (Angiotensin Converting Enzyme, Aminopeptidase P). Progesterone can increase the levels of Aminopeptidase P (AP-P), thereby increasing the breakdown of bradykinin, which increases the risk of developing hypertension.[65]
Two large cohort studies published in 2010 both found a significant reduction in adjusted relative risk of all-cause mortality in ever-users of OCs compared to never-users.[2][48]
Other side effects associated with low-dose COCPs are leukorrhea (increased vaginal secretions), reductions in menstrual flow, mastalgia (breast tenderness), and decrease in acne. Side effects associated with older high-dose COCPs include nausea, vomiting, increases in blood pressure, and melasma (facial skin discoloration); these effects are not strongly associated with low-dose formulations.
Excess estrogen, such as from birth control pills, appears to increase cholesterol levels in bile and decrease gallbladder movement, which can lead to gallstones.[66] Progestins found in certain formulations of oral contraceptive pills can limit the effectiveness of weight training to increase muscle mass.[67] This effect is caused by the ability of some progestins to inhibit androgen receptors. One study claims that the pill may affect what male body odors a woman prefers, which may in turn influence her selection of partner.[68] Use of combined oral contraceptives is associated with a reduced risk of endometriosis, giving a relative risk of endometriosis of 0.63 during active use, yet with limited quality of evidence according to a systematic review.[69]
Combined oral contraception decreases total testosterone levels by approximately 0.5 nmol/l, free testosterone by approximately 60%, and increases the amount of sex hormone binding globulin (SHBG) by approximately 100 nmol/l. Contraceptives containing second generation progestins and/or estrogen doses of around 20 –25 mg EE were found to have less impact on SHBG concentrations.[70]
Combined oral contraceptives are generally accepted to be 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 hypercholesterolemia (high cholesterol level), and in smokers over age 40.
COC are also contraindicated for women with liver tumors, hepatic adenoma or severe cirrhosis of the liver, those who have migraine with aura and for those with known or suspected breast cancer. (WHO category 4).
Combined oral contraceptive pills were developed to prevent ovulation by suppressing the release of gonadotropins. Combined hormonal contraceptives, including COCPs, inhibit follicular development and prevent ovulation as a primary mechanism of action.[71][72][73][74]
Progestogen negative feedback decreases the pulse frequency of gonadotropin-releasing hormone (GnRH) release by the hypothalamus, which decreases the secretion of follicle-stimulating hormone (FSH) and greatly decreases the secretion of luteinizing hormone (LH) by the anterior pituitary. Decreased levels of FSH inhibit follicular development, preventing an increase in estradiol levels. Progestogen negative feedback and the lack of estrogen positive feedback on LH secretion prevent a mid-cycle LH surge. Inhibition of follicular development and the absence of a LH surge prevent ovulation.[71][72][73]
Estrogen was originally included in oral contraceptives for better cycle control (to stabilize the endometrium and thereby reduce the incidence of breakthrough bleeding), but was also found to inhibit follicular development and help prevent ovulation. Estrogen negative feedback on the anterior pituitary greatly decreases the secretion of FSH, which inhibits follicular development and helps prevent ovulation.[71][72][73]
Another primary mechanism of action of all progestogen-containing contraceptives is inhibition of sperm penetration through the cervix into the upper genital tract (uterus and fallopian tubes) by decreasing the water content and increasing the viscosity of the cervical mucus.[71]
The estrogen and progestogen in COCPs have other effects on the reproductive system, but these have not been shown to contribute to their contraceptive efficacy:[71]
Insufficient evidence exists on whether changes in the endometrium could actually prevent implantation. The primary mechanisms of action are so effective that the possibility of fertilization during COCP use is very small. Since pregnancy occurs despite endometrial changes when the primary mechanisms of action fail, endometrial changes are unlikely to play a significant role, if any, in the observed effectiveness of COCPs.[71]
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 one week to the next.
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,[75][76][77][78] but obtaining them from European pharmaceutical companies produced from animal extracts was extraordinarily expensive.[79]
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, the saponin from inedible Mexican yams (Dioscorea mexicana and Dioscorea composita) found in the rain forests of Veracruz near Orizaba. The saponin could be converted in the lab to its aglycone moiety diosgenin. 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. When he left Syntex a year later the trade of the barbasco yam had started and the period of the heyday of the Mexican steroid industry had been started. Syntex broke the monopoly of European pharmaceutical companies on steroid hormones, reducing the price of progesterone almost 200-fold over the next eight years.[21][79][80][81][82][83][84][85][86][87][88][89][90]
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.[83]
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.[79][84][91]
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.[84][92]
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 5–30 mg/day) and progesterone (50–300 mg/day) and within the following four months an encouraging 15% became pregnant.[84][85][93]
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 5–24 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.[94]
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.[95]
Chemists Carl Djerassi, Luis Miramontes, 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.[79]
In December 1954, Rock began the first studies of the ovulation-suppressing potential of 5–50 mg doses of the three oral progestins for three months (for 21 days per cycle—days 5–25 followed by pill-free days to produce withdrawal bleeding) in fifty of his infertility patients in Brookline, Massachusetts. Norethindrone or norethynodrel 5 mg doses 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.[96][97]
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.[97][98]
The first contraceptive trial of Enovid led by Celso-Ramón García and Edris Rice-Wray began in April 1956 in Río Piedras, Puerto Rico.[99][100][101][102][103][104][105] A second contraceptive trial of Enovid (and norethindrone) led by Edward T. Tyler began in June 1956 in Los Angeles.[82][106] 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.[107]
On June 10, 1957, the Food and Drug Administration (FDA) approved Enovid 10 mg (9.85 mg norethynodrel and 150 µg 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, and did so on June 23, 1960. At that point, Enovid 10 mg had been in general use for three years and, by conservative estimate, at least half a million women had used it.[86][102][108]
Although FDA-approved for contraceptive use, Searle never marketed Enovid 10 mg as a contraceptive. Eight months later, on February 15, 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 µg mestranol) to physicians as a contraceptive.[86][87]
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.[83][87]
The first published case report of a blood clot and pulmonary embolism in a woman using Enavid (Enovid 10 mg in the U.S.) at a dose of 20 mg/day did not appear until November 1961, four years after its approval, by which time it had been used by over one million women.[102][109][110] 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.[86] 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 Nelson Pill Hearings called by Senator Gaylord Nelson.[111] 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.[87] 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.[112][113][114] 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.[21][86][87]
The first oral contraceptive introduced outside the United States was Schering's Anovlar (norethindrone acetate 4 mg + ethinyl estradiol 50 µg) on January 1, 1961 in Australia.[115]
The first oral contraceptive introduced in Europe was Schering's Anovlar on June 1, 1961 in West Germany.[115] The lower hormonal dose, still in use, was studied by the Belgian Gynaecologist Ferdinand Peeters.[116][117]
Before the mid-1960s, the United Kingdom did not require pre-marketing approval of drugs. The British Family Planning Association (FPA) through its clinics was then the primary provider of family planning services in Britain and provided only contraceptives that were on its Approved List of Contraceptives (established in 1934). In 1957, Searle began marketing Enavid (Enovid 10 mg in the U.S.) for menstrual disorders. Also in 1957, the FPA established a Council for the Investigation of Fertility Control (CIFC) to test and monitor oral contraceptives which began animal testing of oral contraceptives and in 1960 and 1961 began three large clinical trials in Birmingham, Slough, and London.[102][118]
In March 1960, the Birmingham FPA began trials of norethynodrel 2.5 mg + mestranol 50 µg, but a high pregnancy rate initially occurred when the pills accidentally contained only 36 µg of mestranol—the trials were continued with norethynodrel 5 mg + mestranol 75 µg (Conovid in Britain, Enovid 5 mg in the U.S.).[119] In August 1960, the Slough FPA began trials of norethynodrel 2.5 mg + mestranol 100 µg (Conovid-E in Britain, Enovid-E in the U.S.).[120] In May 1961, the London FPA began trials of Schering's Anovlar.[121]
In October 1961, at the recommendation of the Medical Advisory Council of its CIFC, the FPA added Searle's Conovid to its Approved List of Contraceptives.[122] On December 4, 1961, Enoch Powell, then Minister of Health, announced that the oral contraceptive pill Conovid could be prescribed through the NHS at a subsidized price of 2s per month.[123][124] In 1962, Schering's Anovlar and Searle's Conovid-E were added to the FPA's Approved List of Contraceptives.[102][120][121]
On December 28, 1967, the Neuwirth Law legalized contraception in France, including the pill.[125] The pill is the most popular form of contraception in France, especially among young women. It accounts for 60% of the birth control used in France. The abortion rate has remained stable since the introduction of the pill.[126]
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 (STI) rates.[127] As of 2004, condoms accounted for 80% of birth control use in Japan, and this may explain Japan's comparatively low rates of AIDS.[12]
The Pill was approved for use in June 1999. According to estimates, only 1.3 percent of 28 million Japanese females use the Pill, compared with 15.6 percent in the United States. 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. However, as far back as 2007, many Japanese OBGYNs now only require a yearly visit for pill users, with the tri-annual visits only recommended to those who are older or at increased risk of side effects.[12]
The Pill was approved by the FDA in the early 1960s; its use spread rapidly in the late part of that decade, generating an enormous social impact. Time magazine placed the pill on its cover in April, 1967.[128] In the first place, it was more effective than most previous reversible methods of birth control, giving women unprecedented control over their fertility.[citation needed] Its use was separate from intercourse, requiring no special preparations at the time of sexual activity that might interfere with spontaneity or sensation, and the choice to take the Pill was a private one. This combination of factors served to make the Pill immensely popular within a few years of its introduction.[80][87] Claudia Goldin, among others, argue that this new contraceptive technology was a key player in forming women's modern economic role, in that it prolonged the age at which women first married allowing them to invest in education and other forms of human capital as well as generally become more career-oriented. Soon after the birth control pill was legalized, there was a sharp increase in college attendance and graduation rates for women.[129] From an economic point of view, the birth control pill reduced the cost of staying in school. The ability to control fertility without sacrificing sexual relationships allowed women to make long term educational and career plans.
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 the stated teaching on birth control in the 1968 papal encyclical Humanae Vitae. The encyclical reiterated the established Catholic teaching that artificial contraception distorts the nature and purpose of sex.[130]
The United States Senate began hearings on the Pill in 1970 and there were different viewpoints heard from medical professionals. Dr. Michael Newton, President of the College of Obstetricians and Gynecologists said:
"The evidence is not yet clear that these still do in fact cause cancer or related to it. The FDA Advisory Committee made comments about this, that if there wasn't enough evidence to indicate whether or not these pills were related to the development of cancer, and I think that's still thin; you have to be cautious about them, but I don't think there is clear evidence, either one way or the other, that they do or don't cause cancer."[131]
Another physician, Dr. Roy Hertz of the Population Council, said that anyone who takes this should know of "our knowledge and ignorance in these matters" and that all women should be made aware of this so she can decide to take the Pill or not.[131]
The Secretary of Health, Education, and Welfare at the time, Robert Finch announced the federal government had accepted a compromise warning statement which would accompany all sales of birth control pills.[131]
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. According to writer Margaret Wente, "The pill decoupled sex and marriage, and it also decoupled marriage and procreation. The purpose of marriage was mutual satisfaction, not children, and once that happened, gay marriage probably became inevitable."[132]
A woman using COCPs excretes from her urine and feces natural estrogens, estrone (E1) and estradiol (E2), and synthetic estrogen ethinylestradiol (EE2).[133] These hormones can pass through water treatment plants and into rivers.[134] Other forms of contraception, such as the contraceptive patch, use the same synthetic estrogen (EE2) that is found in COCPs, and can add to the hormonal concentration in the water when flushed down the toilet.[135] This excretion is shown to play a role in causing endocrine disruption, which affects the sexual development and the reproduction, in wild fish populations in segments of streams contaminated by treated sewage effluents.[133][136] A study done in British rivers supported the hypothesis that the incidence and the severity of intersex wild fish populations were significantly correlated with the concentrations of the E1, E2, and EE2 in the rivers.[133]
A review of activated sludge plant performance found estrogen removal rates varied considerably but averaged 78% for estrone, 91% for estradiol, and 76% for ethinylestradiol (estriol effluent concentrations are between those of estrone and estradiol, but estriol is a much less potent endocrine disruptor to fish).[137] Effluent concentrations of ethinylestradiol are lower than estradiol which are lower than estrone, but ethinylestradiol is more potent than estradiol which is more potent than estrone in the induction of intersex fish and synthesis of vitellogenin in male fish.[138]
|accessdate= requires |url= (help)|displayauthors= suggested (help)Mechanism of action
COCs prevent fertilization and, therefore, qualify as contraceptives. There is no significant evidence that they work after fertilization. The progestins in all COCs provide most of the contraceptive effect by suppressing ovulation and thickening cervical mucus, although the estrogens also make a small contribution to ovulation suppression. Cycle control is enhanced by the estrogen.
Because COCs so effectively suppress ovulation and block ascent of sperm into the upper genital tract, the potential impact on endometrial receptivity to implantation is almost academic. When the two primary mechanisms fail, the fact that pregnancy occurs despite the endometrial changes demonstrates that those endometrial changes do not significantly contribute to the pill's mechanism of action.
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| リンク元 | 「混合経口避妊薬」 |
| 関連記事 | 「combine」「oral」「contraceptive」「combined」 |