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 backup contraceptive methods during antibiotic use. Examples of medications that increase the elimination of estrogens include
- carbamazepine (Tegretol),
- 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 seven per 10,000 cases of exposure during pregnancy to oral contraceptives), but a clear association with fetal abnormalities has not been firmly established. Modified development of the sexual organs occurs somewhat more frequently, in about three per 1,000 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.
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