Estrogens appear to increase the risk of liver disease in patients receiving dantrolene (Dantrium) through an unknown mechanism. Women over 35 years of age and those with a history of liver disease are especially at risk.

Estrogens increase the liver's ability to manufacture clotting factors. Because of this, patients receiving warfarin (Coumadin) need to be monitored for loss of anticoagulant (blood thinning) effect if an estrogen is begun.

A number of medications, including some antibiotics and antiseizure medications, can decrease the blood levels of oral contraceptive hormones, but an actual decrease in the effectiveness of the oral contraceptive has not been convincingly proven. Nonetheless, because of this theoretical possibility, some physicians recommend back-up contraceptive methods during antibiotic use. Examples of medications that increase the elimination of estrogens include:

• carbamazepine (Tegretol),
  
  
• phenobarbital,
  
  
• phenytoin (Dilantin),
  
  
• primidone (Mysoline),
  
  
• rifampin (Rifadin),
  
  
• rifabutin (Mycobutin), and
  
  
• ritonavir (Norvir).

Birth control pills with higher concentrations of estrogen or alternative forms of contraception may be necessary in women using those medications.

PREGNANCY: Rarely, fetal abnormalities (including those of the vertebrae, anus, heart, trachea, esophagus, kidney, and limbs) have been reported (in about 7 per 10,000 cases of exposure during pregnancy to oral contraceptives), but the clear association with fetal abnormalities has not been firmly established. Modified development of the sexual organs occurs somewhat more frequently, in about three per 1000 cases of exposure. Specifically, masculinization of female infants has been reported with norethindrone and norethynodrel. Increased blood bilirubin concentrations and jaundice have been reported in infants born to women who took oral contraceptives shortly before and after conception.

NURSING MOTHERS: Use of birth control pills during lactation has been associated with decreased milk production, decreased infant weight gain, and decreased nitrogen and protein content of milk. The amount of estrogen consumed by an infant whose mother takes a standard dose of birth control pills is considered to be the same as from a lactating woman who is not taking birth control pills, and side effects have not been reported. Using a progestin-only product is most often recommended during lactation if birth control pills are to be used during this period. The American College of Obstetrics and Gynecology (ACOG) recommends delaying taking combined estrogen-progestin contraceptives until at least six weeks postpartum, while the World Health Organization (WHO) recommends delaying the initiation of combined contraceptives until six months.

SIDE EFFECTS: The most common side effects of the birth control pills include nausea, headache, breast tenderness, weight gain, irregular bleeding, and mood changes. These side effects often subside after a few months' use. Scanty menstrual periods or breakthrough bleeding may occur, but are often temporary, and neither side effect is serious. Women with a history of migraines may notice an increase in migraine frequency. On the other hand, women whose migraines are triggered by fluctuations in their own hormone levels may notice improvement in migraines with oral contraceptive use because of the more uniform hormone levels during oral contraceptive use. Uncommonly, oral contraceptives may contribute to increased blood pressure, blood clots, heart attack, and stroke. Women who smoke, especially those over 35, and women with certain medical conditions, such as a history of blood clots or breast or endometrial cancer, may be advised against taking oral contraceptives, as these conditions can increase the adverse risks of oral contraceptives.

The following table contains examples of oral contraceptives of different categories:

Previous contributing medical author: Carolyn Janet Crandall, MD, FACP
Last Editorial Review: 7/14/2008

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