"What are birth control pills and how do they work?
Birth control pills are also known as oral contraceptives (OCs) or, simply, “the pill.” They offer protection against pregnancy by blocking the union of sperm and egg, thereby prevent"...
Cigarette smoking increases the risk of serious cardiovascular side effects from oral contraceptive use. This risk increases with age and with heavy smoking (15 or more cigarettes per day) and is quite marked in women over 35 years of age. Women who use oral contraceptives should be strongly advised not to smoke.
The use of oral contraceptives is associated with increased risk of several serious conditions including venous and arterial thromboembolism, thrombotic and hemorrhagic stroke, myocardial infarction, liver tumors or other liver lesions, and gallbladder disease. The risk of morbidity and mortality increases significantly in the presence of other risk factors such as hypertension, hyperlipidemia, obesity, and diabetes mellitus.
Practitioners prescribing oral contraceptives should be familiar with the following information relating to these and other risks.
The information contained herein is principally based on studies carried out in patients who used oral contraceptives with formulations containing higher amounts of estrogens and progestogens than those in common use today. The effect of long-term use of the oral contraceptives with lesser amounts of both estrogens and progestogens remains to be determined.
Throughout this labeling, epidemiological studies reported are of two types: retrospective case-control studies and prospective cohort studies. Case-control studies provide an estimate of the relative risk of a disease, which is defined as the ratio of the incidence of a disease among oral contraceptive users to that among nonusers. The relative risk (or odds ratio) does not provide information about the actual clinical occurrence of a disease. Cohort studies provide a measure of both the relative risk and the attributable risk. The latter is the difference in the incidence of disease between oral contraceptive users and nonusers. The attributable risk does provide information about the actual occurrence or incidence of a disease in the subject population. For further information, the reader is referred to a text on epidemiological methods.
Thromboembolic disorders and other vascular problems.
An increased risk of myocardial infarction has been associated with oral contraceptive use.2-21 This increased risk is primarily in smokers or in women with other underlying risk factors for coronary artery disease such as hypertension, obesity, diabetes, and hypercholesterolemia. The relative risk for myocardial infarction in current oral contraceptive users has been estimated to be 2 to 6. The risk is very low under the age of 30. However, there is the possibility of a risk of cardiovascular disease even in very young women who take oral contraceptives.
Smoking in combination with oral contraceptive use has been reported to contribute substantially to the risk of myocardial infarction in women in their mid-thirties or older, with smoking accounting for the majority of excess cases.22 Mortality rates associated with circulatory disease have been shown to increase substantially in smokers, especially in those 35 years of age and older among women who use oral contraceptives (See Figure 1, Table 2).
Figure 1. Circulatory disease mortality rates per 100,000
woman-years by age, smoking status, and oral contraceptive use.14
Adapted from Layde and Beral.14
Oral contraceptives may compound the effects of well-known cardiovascular risk factors such as hypertension, diabetes, hyperlipidemias, hypercholesterolemia, age, cigarette smoking, and obesity. In particular, some progestogens decrease HDL cholesterol23-31 and cause glucose intolerance, while estrogens may create a state of hyperinsulinism.32 Oral contraceptives have been shown to increase blood pressure among some users (See WARNINGS). Similar effects on risk factors have been associated with an increased risk of heart disease.
An increased risk of thromboembolic and thrombotic disease associated with the use of oral contraceptives is well established.17, 33-51 Case-control studies have estimated the relative risk to be 3 for the first episode of superficial venous thrombosis, 4 to 11 for deep vein thrombosis or pulmonary embolism, and 1.5 to 6 for women with predisposing conditions for venous thromboembolic disease.34-37, 45, 46 Cohort studies have shown the relative risk to be somewhat lower, about 3 for new cases (subjects with no past history of venous thrombosis or varicose veins) and about 4.5 for new cases requiring hospitalization.42, 47, 48 The risk of venous thromboembolic disease associated with oral contraceptives is not related to duration of use.
A two- to seven-fold increase in relative risk of postoperative thromboembolic complications has been reported with the use of oral contraceptives.38, 39 The relative risk of venous thrombosis in women who have predisposing conditions is about twice that of women without such medical conditions.43 If feasible, oral contraceptives should be discontinued at least 4 weeks prior to and for 2 weeks after elective surgery of a type associated with an increased risk of thromboembolism, and also during and following prolonged immobilization. Since the immediate postpartum period is also associated with an increased risk of thromboembolism, oral contraceptives should be started no earlier than 4 to 6 weeks after delivery in women who elect not to breast feed.
Both the relative and attributable risks of cerebrovascular events (thrombotic and hemorrhagic strokes) have been reported to be increased with oral contraceptive use,14, 17, 18, 34, 42, 46, 52-59 although, in general, the risk was greatest among older (over 35 years), hypertensive women who also smoked. Hypertension was reported to be a risk factor for both users and nonusers, for both types of strokes, while smoking increased the risk for hemorrhagic strokes.
In one large study,52 the relative risk for thrombotic stroke was reported as 9.5 times greater in users than in nonusers. It ranged from 3 for normotensive users to 14 for users with severe hypertension.54 The relative risk for hemorrhagic stroke was reported to be 1.2 for nonsmokers who used oral contraceptives, 1.9 to 2.6 for smokers who did not use oral contraceptives, 6.1 to 7.6 for smokers who used oral contraceptives, 1.8 for normotensive users, and 25.7 for users with severe hypertension. The risk is also greater in older women and among smokers.
Dose-related risk of vascular disease with oral contraceptives
A positive association has been reported between the amount of estrogen and progestogen in oral contraceptives and the risk of vascular disease.41, 43, 53, 59-64 A decline in serum high density lipoproteins (HDL) has been reported with many progestogens.23-31 A decline in serum high density lipoproteins has been associated with an increased incidence of ischemic heart disease.65 Because estrogens increase HDL-cholesterol, the net effect of an oral contraceptive depends on the balance achieved between doses of estrogen and progestogen and the nature and absolute amount of progestogens used in the contraceptives. The amount of both steroids should be considered in the choice of an oral contraceptive.
Minimizing exposure to estrogen and progestogen is in keeping with good principles of therapeutics. For any particular estrogenprogestogen combination, the dosage regimen prescribed should be one that contains the least amount of estrogen and progestogen that is compatible with a low failure rate and the needs of the individual patient. New acceptors of oral contraceptives should be started on preparations containing the lowest estrogen content that produces satisfactory results in the individual.
Products containing 50 mcg estrogen should be used only when medically indicated.
Persistence of risk of vascular diseas
There are three studies that have shown persistence of risk of vascular disease for users of oral contraceptives. In a study in the United States, the risk of developing myocardial infarction after discontinuing oral contraceptives persisted for at least 9 years for women 40-49 years old who had used oral contraceptives for 5 or more years, but this increased risk was not demonstrated in other age groups.16 Another American study reported former use of oral contraceptives was significantly associated with increased risk of subarachnoid hemorrhage.57 In another study, in Great Britain, the risk of developing nonrheumatic heart disease plus hypertension, subarachnoid hemorrhage, cerebral thrombosis, and transient ischemic attacks persisted for at least 6 years after discontinuation of oral contraceptives, although the excess risk was small.14, 18, 66 It should be noted that these studies were performed with oral contraceptive formulations containing 50 mcg or more of estrogens.
Estimates of mortality from contraceptive use
One study67 gathered data from a variety of sources that have estimated the mortality rates associated with different methods of contraception at different ages (Table 2). These estimates include the combined risk of death associated with contraceptive methods plus the risk attributable to pregnancy in the event of method failure. Each method of contraception has its specific benefits and risks. The study concluded that, with the exception of oral contraceptive users 35 and older who smoke and 40 or older who do not smoke, mortality associated with all methods of birth control is low and below that associated with childbirth. The observation of a possible increase in risk of mortality with age for oral contraceptive users is based on data gathered in the 1970's, but not reported until 1983.67 However, current clinical practice involves the use of lower estrogen dose formulations combined with careful restriction of oral contraceptive use to women who do not have the various risk factors listed in this labeling.
Because of these changes in practice and, also, because of some limited new data that suggest that the risk of cardiovascular disease with the use of oral contraceptives may now be less than previously observed,48, 152 the Fertility and Maternal Health Drugs Advisory Committee was asked to review the topic in 1989. The Committee concluded that, although cardiovascular disease risks may be increased with oral contraceptive use after age 40 in healthy nonsmoking women (even with the newer low-dose formulations), there are greater potential health risks associated with pregnancy in older women and with the alternative surgical and medical procedures that may be necessary if such women do not have access to effective and acceptable means of contraception.
Therefore, the Committee recommended that the benefits of oral contraceptive use by healthy nonsmoking women over 40 may outweigh the possible risks. Of course, older women, as all women who take oral contraceptives, should take the lowest possible dose formulation that is effective.
Table 2. Annual number of birth-related or method-related
deaths associated with control of fertility per 100,000 nonsterile women, by
fertility control method according to age.67
|Method of control||Age|
|No fertility control methods*||7||7.4||9.1||14.8||25.7||28.2|
| *Deaths are birth-related
**Deaths are method-related
Adapted from Ory.67
Carcinoma of the breast and reproductive organs
Numerous epidemiological studies have been performed on the incidence of breast, endometrial, ovarian, and cervical cancer in women using oral contraceptives. While there are conflicting reports, many studies suggest that the use of oral contraceptives is not associated with an overall increase in the risk of developing breast cancer.17,40,68–78 Other studies, however, have reported an increased risk overall,153–155 or in certain subgroups. In these studies, increased risk has been associated with long duration of use, use beginning at a young age, use before the first term pregnancy, use by those who had an early menarche, those who had a positive family history of breast cancer, or in nulliparas.79–102,151,156–162 These risks have been surveyed in two books163–164 and in review articles.85,99,153,165–167
Some studies suggested that oral contraceptive use was associated with an increase in the risk of cervical intraepithelial neoplasia, dysplasia, erosion, carcinoma, or micro-glandular dysplasia in some populations of women.17, 50, 103-115 However, there continues to be controversy about the extent to which such findings may be due to differences in sexual behavior and other factors.
In spite of many studies of the relationship between oral contraceptive use and breast and cervical cancers, a cause and effect relationship has not been established.
Benign hepatic adenomas and other hepatic lesions have been associated with oral contraceptive use,116-121 although the incidence of such benign tumors is rare in the United States. Indirect calculations have estimated the attributable risk to be in the range of 3.3 cases per 100,000 for users, a risk that increases after 4 or more years of use.120 Rupture of benign, hepatic adenomas or other lesions may cause death through intraabdominal hemorrhage. Therefore, such lesions should be considered in women presenting with abdominal pain and tenderness, abdominal mass, or shock. About one quarter of the cases presented because of abdominal masses; up to one half had signs and symptoms of acute intraperitoneal hemorrhage.121Diagnosis may prove difficult.
Studies from the U.S.,122, 150 Great Britain,123, 124 and Italy125 have shown an increased risk of hepatocellular carcinoma in long-term ( > 8 years; relative risk of 7-20) oral contraceptive users. However, these cancers are rare in the United States, and the attributable risk (the excess incidence) of liver cancers in oral contraceptive users approaches less than 1 per 1,000,000 users.
There have been reports of retinal thrombosis and other ocular lesions associated with the use of oral contraceptives. Oral contraceptives should be discontinued if there is unexplained, gradual or sudden, partial or complete loss of vision; onset of proptosis or diplopia; papilledema; or any evidence of retinal vascular lesions. Appropriate diagnostic and therapeutic measures should be undertaken immediately.
Oral contraceptive use before or during pregnancy
Extensive epidemiological studies have revealed no increased risk of birth defects in women who have used oral contraceptives prior to pregnancy.126, 129 The majority of recent studies also do not suggest a teratogenic effect, particularly insofar as cardiac anomalies and limb reduction defects are concerned,126, 129 when the pill is taken inadvertently during early pregnancy.
The administration of oral contraceptives to induce withdrawal bleeding should not be used as a test for pregnancy. Oral contraceptives should not be used during pregnancy to treat threatened or habitual abortion. It is recommended that for any patient who has missed two consecutive periods, pregnancy should be ruled out before continuing oral contraceptive use. If the patient has not adhered to the prescribed schedule, the possibility of pregnancy should be considered at the time of the first missed period and further use of oral contraceptives should be withheld until pregnancy has been ruled out. Oral contraceptive use should be discontinued if pregnancy is confirmed.
Earlier studies reported an increased lifetime relative risk of gallbladder surgery in users of oral contraceptives and estrogens.40, 42, 53, 70 More recent studies, however, have shown that the relative risk of developing gallbladder disease among oral contraceptive users may be minimal.130-132 The recent findings of minimal risk may be related to the use of oral contraceptive formulations containing lower doses of estrogens and progestogens.
Carbohydrate and lipid metabolic effects
Oral contraceptives have been shown to cause a decrease in glucose tolerance in a significant percentage of users.32 This effect has been shown to be directly related to estrogen dose.133 Progestogens increase insulin secretion and create insulin resistance, the effect varying with different progestational agents.32, 134 However, in the nondiabetic woman, oral contraceptives appear to have no effect on fasting blood glucose. Because of these demonstrated effects, prediabetic and diabetic women should be carefully observed while taking oral contraceptives.
Some women may have persistent hypertriglyceridemia while on the pill. As discussed earlier (See WARNINGS), changes in serum triglycerides and lipoprotein levels have been reported in oral contraceptive users.23-31, 135, 136
Elevated blood pressure
An increase in blood pressure has been reported in women taking oral contraceptives50, 53, 137-139 and this increase is more likely in older oral contraceptive users137 and with extended duration of use.53 Data from the Royal College of General Practitioners138 and subsequent randomized trials have shown that the incidence of hypertension increases with increasing concentrations of progestogens.
Women with a history of hypertension or hypertension-related disease, or renal disease139 should be encouraged to use another method of contraception. If such women elect to use oral contraceptives, they should be monitored closely and if significant elevation of blood pressure occurs, oral contraceptives should be discontinued. For most women, elevated blood pressure will return to normal after stopping oral contraceptives,137 and there is no difference in the occurrence of hypertension among everand never-users.140
The onset or exacerbation of migraine or the development of headache of a new pattern that is recurrent, persistent, or severe requires discontinuation of oral contraceptives and evaluation of the cause.
Breakthrough bleeding and spotting are sometimes encountered in patients on oral contraceptives, especially during the first three months of use. Nonhormonal causes should be considered and adequate diagnostic measures taken to rule out malignancy or pregnancy in the event of breakthrough bleeding, as in the case of any abnormal vaginal bleeding. If a pathologic basis has been excluded, time alone or a change to another formulation may solve the problem. In the event of amenorrhea, pregnancy should be ruled out. Some women may encounter post-pill amenorrhea or oligomenorrhea, especially when such a condition was pre-existent.
Physical examination and follow-up
It is good medical practice for all women to have annual history and physical examinations, including women using oral contraceptives. The physical examination, however, may be deferred until after initiation of oral contraceptives if requested by the woman and judged appropriate by the clinician. The physical examination should include special reference to blood pressure, breasts, abdomen, and pelvic organs, including cervical cytology, and relevant laboratory tests. In case of undiagnosed, persistent, or recurrent abnormal vaginal bleeding, appropriate measures should be conducted to rule out malignancy. Women with a strong family history of breast cancer or who have breast nodules should be monitored with particular care.
Women who are being treated for hyperlipidemias should be followed closely if they elect to use oral contraceptives. Some progestogens may elevate LDL levels and may render the control of hyperlipidemias more difficult.
If jaundice develops in any woman receiving oral contraceptives, they should be discontinued. Steroids may be poorly metabolized in patients with impaired liver function and should be administered with caution in such patients. Cholestatic jaundice has been reported after combined treatment with oral contraceptives and troleandomycin. Hepatotoxicity following a combination of oral contraceptives and cyclosporine has also been reported.
Oral contraceptives may cause some degree of fluid retention. They should be prescribed with caution, and only with careful monitoring, in patients with conditions that might be aggravated by fluid retention, such as convulsive disorders, migraine syndrome, asthma, or cardiac, hepatic, or renal dysfunction.
Women with a history of depression should be carefully observed and the drug discontinued if depression recurs to a serious degree.
Contact lens wearers who develop visual changes or changes in lens tolerance should be assessed by an ophthalmologist.
Pregnancy Category X. (See CONTRAINDICATIONS and WARNINGS.)
Small amounts of oral contraceptive steroids have been identified in the milk of nursing mothers141-143 and a few adverse effects on the child have been reported, including jaundice and breast enlargement. In addition, oral contraceptives given in the postpartum period may interfere with lactation by decreasing the quantity and quality of breast milk. If possible, the nursing mother should be advised not to use oral contraceptives, but to use other forms of contraception until she has completely weaned her child.
Safety and efficacy of Zovia (ehtynodiol diacetate and ethinyl estradiol tablets) have been established in women of reproductive age. Safety and efficacy are expected to be the same for postpubertal adolescents under the age of 16 and for users 16 years and older. Use of this product before menarche is not indicated.
Oral contraceptives are of no value in the prevention or treatment of venereal disease. The prevalence of cervical Chlamydia trachomatis and Neisseria gonorrhoeae in oral contraceptive users is increased several-fold.144, 145 It should not be assumed that oral contraceptives afford protection against pelvic inflammatory disease from chlamydia.144 Patients should be counseled that this product does not protect against HIV infection (AIDS) and other sexually transmitted diseases.
- The pathologist should be advised of oral contraceptive therapy when relevant specimens are submitted.
- Treatment with oral contraceptives may mask the onset of the climacteric. (See WARNINGS regarding risks in this age group.)
Information for the Patient
See patient labeling.
1. Hatcher RA, et al. Contraceptive Technology: Seventeenth
Revised Edition. New York, NY, 1998. 1a.Physicians' Desk Reference. 47th ed.
Oradell, NJ: Medical Economics Co Inc; 1993;2598-2601.
2. Mann JI, et al. Br Med J. 1975; 2 (May 3):241.
3. Mann JI, et al. Br Med J. 1975;3(Sept 13):631.
4. Mann JI, et al. Br Med J. 1975;2(May 3):245.
5. Mann JI, et al. Br Med J. 1976;2(Aug 21):445.
6. Arthes FG, et al. Chest. 1976;70 (Nov):574.
7. Jain AK, Am J Obstet Gynecol. 1976;301(Oct 1):126 and Stud
Fam Plann. 1977;8(March):50.
8. Ory HW. JAMA. 1977;237(June 13):2619.
9. Jick H, et al. JAMA. 1978;239(April 3):1403, 1407.
10. Jick H, et al. JAMA. 1978;240(Dec 1):2548.
11. Shapiro S, et al. Lancet. 1979;1(April 7):743.
12. Rosenberg L, et al. Am J Epidemiol. 1980;111(Jan):59.
13. Krueger DE, et al. Am J Epidemiol. 1980;111 (June):655.
14. Layde P, et al. Lancet. 1981;1(March 7):541.
15. Adam SA, et al. Br J Obstet Gynaecol. 1981;88(Aug):838.
16. Slone D, et al. N Engl J Med. 1981;305 (Aug 20):420.
17. Ramcharan S, et al. The Walnut Creek Contraceptive Drug
Study. Vol 3. US Govt Ptg Off. 1981; and J Reprod Med. 1980;25(Dec):346.
18. Layde PM, et al. J R Coll Gen Pract. 1983;33(Feb):75.
19. Rosenberg L, et al. JAMA. 1985;253(May 24/31):2965.
20. Mant D, et al. J Epidemiol Community Health. 1987;41 (Sept):215.
21. Croft P, et al. Br Med J. 1989;298 (Jan 21):165.
22. Goldbaum GM, et al. JAMA. 1987;258(Sept 11):1339.
23. Bradley DD, et al. N Engl J Med. 1978;299(July 6):17.
24. Tikkanen MJ. J Reprod Med. 1986;31(Sept suppl):898.
25. Lipson A, et al. Contraception. 1986;34(Aug):121.
26. Burkman RT, et al. Obstet Gynecol. 1988; 71(Jan):33.
27. Knopp RH, J Reprod Med. 1986;31(Sept Suppl):913.
28. Krauss RM, et al. Am J Obstet Gynecol. 1983;145(Feb 15):446.
29. Wahl P, et al. N Engl J Med. 1983;308(April 14):862.
30. Wynn V, et al. Am J Obstet Gynecol. 1982;142(March 15):766.
31. LaRosa JC. J Reprod Med. 1986;31(Sept suppl):906.
32. Wynn V, et al. J Reprod Med. 1986;31(Sept Suppl):892.
33. Royal College of General Practitioners. J R Coll Gen Pract.
34. Inman WHW, et al. Br Med J. 1968;2(April 27):193.
35. Vessey MP, et al. Br Med J. 1968;2(April 27):199.
36. Vessey MP, et al. Br Med J. 1969;2(June 14):651.
37. Sartwell PE, et al. Am J Epidemiol. 1969;90(Nov):365.
38. Vessey MP, et al. Br Med J. 1970;3(July 18):123.
39. Greene GR, et al. Am J Public Health. 1972;62(May):680.
40. Boston Collaborative Drug Surveillance Programme. Lancet.
41. Stolley PD, et al. Am J Epidemiol. 1975;102(Sept):197.
42. Vessey MP, et al. J Biosoc Sci. 1976;8(Oct):373.
43. Kay CR, J R Coll Gen Pract. 1978;28(July):393.
44. Petitti DB, et al. Am J Epidemiol. 1978;108 (Dec):480.
45. Maquire MG, et al. Am J Epidemiol. 1979;110(Aug):188.
46. Petitti DB, et al. JAMA. 1979;242(Sept 14):1150.
47. Porter JB, et al. Obstet Gynecol. 1982;59(March):299.
48. Porter JB, et al. Obstet Gynecol. 1985;66(July):1.
49. Vessey MP, et al. Br Med J. 1986;292(Feb 22):526.
50. Hoover R, et al. Am J Public Health. 1978;68(April):335.
51. Vessey MP, Br J Fam Plann. 1980;6(Oct suppl):1.
52. Collaborative Group for the Study of Stroke in Young Women.
N Engl J Med. 1973;288(April 26):871.
53. Royal College of General Practitioners. Oral Contraceptives
and Health. New York, NY: Pitman Publ Corp; May 1974.
54. Collaborative Group for the Study of Stroke in Young Women.
JAMA. 1975;231(Feb 17):718.
55. Beral V. Lancet. 1976;2(Nov 13):1047.
56. Vessey MP, et al. Lancet. 1977;2(Oct 8):731; and 1981;1(March
57. Petitti DB, et al. Lancet. 1978;2(July 29):234.
58. Inman WHW. Br Med J. 1979;2(Dec 8):1468.
59. Vessey MP, et al. Br Med J. 1984; 289(Sept 1):530.
60. Inman WHW, et al. Br Med J. 1970;2(April 25):203.
61. Meade TW, et al. Br Med J. 1980;280(May 10):1157.
62. Böttiger LE, et al. Lancet. 1980;1(May 24):1097.
63. Kay CR. Am J ObstetGynecol. 1982;142(March 15):762.
64. Vessey MP, et al. Br Med J. 1986;292(Feb 22):526.
65. Gordon T, et al. Am J Med. 1977;62(May):707.
66. Beral V, et al. Lancet. 1977;2(Oct 8):727.
67. Ory H. Fam Plann Perspect. 1983;15(March-April):57.
68. Arthes FG, et al. Cancer. 1971;28 (Dec):1391.
69. Vessey MP, et al. Br Med J. 1972;3(Sept 23):719.
70. Boston Collaborative Drug Surveillance Program. N Engl J
Med. 1974;290(Jan 3):15.
71. Vessey MP, et al. Lancet. 1975;1(April 26):941.
72. Casagrande J, et al. J Natl Cancer Inst. 1976;56(April):839.
73. Kelsey, JL, et al. Am J Epidemiol. 1978;107(March):236.
74. Kay CR, Br Med J. 1981;282(June 27):2089.
75. Vessey MP, et al. Br Med J. 1981;282(June 27):2093.
76. The Cancer and Steroid Hormone Study of the Centers for
Disease Control and the National Institute of Child Health and Human Development.
Oral contraceptive use and the risk of breast cancer. N Engl J Med. 1986;315(Aug
77. Paul C, et al. Br Med J. 1986; 293 (Sept 20):723.
78. Miller DR, et al. Obstet Gynecol. 1986;68(Dec):863.
79. Pike MC, et al. Lancet. 1983;2(Oct 22):926.
80. McPherson K, et al. Br J Cancer. 1987;56(Nov):653.
81. Hoover R, et al. N Engl J Med. 1976;295(Aug 19):401.
82. Lees AW, et al. Int J Cancer. 1978;22(Dec):700.
83. Brinton LA, et al. J Natl Cancer Inst. 1979;62(Jan):37.
84. Black MM. Pathol Res Pract. 1980;166:491; and Cancer. 1980;46(Dec):2747;
and Cancer. 1983;51(June):2147.
85. Thomas DB. JNCI. 1993;85 (March 3):359.
86. Brinton LA, et al. Int J Epidemiol. 1982;11(Dec):316.
87. Harris NV, et al. Am J Epidemiol. 1982;116(Oct):643.
88. Jick H, et al. Am J Epidemiol. 1980;112(Nov):577.
89. McPherson K, et al. Lancet. 1983;2(Dec 17):1414.
90. Hoover R, et al. J Natl Cancer Inst. 1981; 67(Oct):815.
91. Jick H, et al. Am J Epidemiol. 1980; 112(Nov):586.
92. Meirik O, et al. Lancet. 1986;2 (Sept 20):650.
93. Fasal E, et al. J Natl Cancer Inst. 1975;55(Oct):767.
94. Paffenbarger RS, et al. Cancer. 1977;39(April suppl):1887.
95. Stadel BV, et al. Contraception. 1988;38(Sept):287.
96. Miller DR, et al. Am J Epidemiol. 1989;129(Feb):269.
97. Kay CR, et al. Br J Cancer. 1988;58(Nov):675.
98. Miller DR, et al. Obstet Gynecol. 1986;68(Dec):863.
99. Hulka BS, et al. Cancer. 1994;74(August 1 suppl):1111.
100. Chilver CED, et al. Br J Cancer. 1994;67(May):922.
101. Huggins GR, et al. Fertil Steril. 1987;47(May):733.
102. Pike MC, et al. Br J Cancer. 1981;43(Jan):72.
103. Ory H, et al. Am J Obstet Gynecol. 1976;124(March 15):573.
104. Stern E, et al. Science. 1977;196(June 24):1460.
105. Pertiz E, et al. Am J Epidemiol. 1977;106(Dec):462.
106. Ory HW, et al. In: Garattini S, Berendes H, eds. Pharmacology
of Steroid Contraceptive Drugs. New York, NY: Raven Press; 1977:211-224.
107. Meisels A, et al. Cancer. 1977;40(Dec):3076.
108. Goldacre MJ, et al. Br Med J. 1978;1(March 25):748.
109. Swan SH, et al. Am J Obstet Gynecol. 1981;139(Jan 1):52.
110. Vessey MP, et al. Lancet. 1983;2(Oct 22):930.
111. Dallenbach-Hellweg G. Pathol Res Pract. 1984;179:38.
112. Thomas DB, et al. Br Med J. 1985;290(March 30):961.
113. Brinton LA, et al. Int J Cancer. 1986;38(Sept):339.
114. Ebeling K, et al. Int J Cancer. 1987;39(April):427.
115. Beral V, et al. Lancet. 1988;2(Dec 10):1331.
116. Baum JK, et al. Lancet. 1973;2(Oct 27):926.
117. Edmondson HA, et al. N Engl J Med. 1976;294(Feb 26):470.
118. Bein NN, et al. Br J Surg. 1977;64(June):433.
119. Klatskin G. Gastroenterology. 1977;73(Aug):386.
120. Rooks JB, et al. JAMA. 1979;242(Aug 17):644.
121. Sturtevant FM. In: Moghissi K, ed. Controversies in Contraception,
Baltimore, MD; Williams & Wilkins; 1979:93-150.
122. Henderson BE, et al. Br J Cancer. 1983;48(July):437.
123. Neuberger J, et al. Br Med J. 1986;292(May 24):1355.
124. Forman D, et al. Br Med J. 1986;292(May 24):1357.
125. La Vecchia C, et al. Br J Cancer. 1989;59(March):460.
126. Savolainen E, et al. Am J Obstet Gynecol 1981;140(July
127. Ferencz C, et al. Teratology. 1980;21(April):225.
128. Rothman KJ, et al. Am J Epidemiol. 1979;109(April):433.
129. Harlap S, et al. Obstet Gynecol. 1980;55(April):447.
130. Layde PM, et al. J Epidemiol Community Health. 1982;36(Dec):274.
131. Rome Group for the Epidemiology and Prevention of Cholelithiasis
(GREPCO). Am J Epidemiol. 1984;119(May):796.
132. Strom BL, et al. Clin Pharmacol Ther. 1986;39(March):335.
133. Wynn V. In: Bardin CE, et al, eds. Progesterone and Progestins.
New York, NY: Raven Press; 1983:395-410.
134. Perlman JA, et al. J Chron Dis. 1985;38(Oct):857.
135. Powell MG, et al. Obstet Gynecol. 1984;63(June):764.
136. Wynn V, et al. Lancet. 1966;2(Oct 1):720.
137. Fisch IR, et al. JAMA. 1977;237(June 6):2499.
138. Kay CR. Lancet. 1977;1(March 19):624.
139. Laragh JH. Am J Obstet Gynecol. 1976;126(Sept 1):141.
140. Ramcharan S. In: Garattini S, Berendes HW, eds. Pharmacology
of Steroid Contraceptive Drugs. New York, NY: Raven Press; 1977:277-288.
141. Laumas KR, et al. Am J Obstet Gynecol. 1967;98(June 1):411.
142. Saxena BN, et al. Contraception. 1977;16(Dec):605.
143. Nilsson S, et al. Contraception. 1978;17(Feb):131.
144. Washington AE, et al. JAMA. 1985;253(April 19):2246.
145. Louv WC, et al. Am J Obstet Gynecol. 1989;160(Feb):396.
150. Palmer JR, et al. Am J Epidemiol. 1989;130(Nov):878.
151. Romieu I, et al. J Natl Cancer Inst. 1989;81(Sept):1313.
152. Porter JB, et al. Obstet Gynecol. 1987;70(July):29.
153. Olsson H, et al. Cancer Detect Prev. 1991;15:265.
154. Delgado- Rodriguez M, et al. Rev Epidém Santé
155. Clavel F, et al. Int J Epidemiol. 1991;20(March):32.
156. Brinton LA, et al. JNCI. 1995;87(June 7):827.
157. Thomas DB, et al. Br J Cancer. 1992;65(January):108.
158. Thomas DB, et al. Cancer Causes Cont. 1991;2(Nov):389.
159. Weinstein AL, et al. Epidemiology. 1991;2(Sept):353.
160. Ranstam J, et al. Anticancer Res. 1991;11(Nov- Dec):2043.
161. Ursin G. et al. Epidemiology. 1992;3(Sept):414.
162. White E, et al. JNCI. 1994;86(April 6):505.
163. Mann R, et al. Oral contraceptives and Breast Cancer. Park
Ridge, NJ: The Parthenon Publishing Group Inc.; 1990.
164. Institute of Medicine. Committee on the Relationship Between
Oral Contraceptives and Breast Cancer. Oral Contraceptives and Breast Cancer.
Washington, DC: National Academy Press; 1991.
165. Harlap S. J Reprod Med. 1991;36(May):374.
166. Rushton L, et al. Br J Obstet Gynaecol. 1992;99(March):239.
167. Colditz G. Cancer. 1993;71(Feb 15 suppl):1480.This monograph has been modified to include the generic and brand name in many instances.
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