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Antibiotics and Birth Control Pill Interactions: Fact or Fallacy?

Medically reviewed on Jun 29, 2015 by L. Anderson, PharmD

Are you concerned when you receive an antibiotic prescription but you also take oral contraceptives? For many years, women were counseled that their birth control pill might become less effective if they also took a course of antibiotic. The usual advice to women from healthcare providers was to use an added form of birth control to their pills, such as a condom, to prevent pregnancy until after the antibiotic was finished.

However, according to the latest available studies, experts and women’s health providers, only one antibiotic - rifampin (Rifadin) - has been proven to make birth control less effective. Rifampin lowers the effectiveness by decreasing the birth control hormone levels (ethinyl estradiol and progestin) in women taking oral contraceptives. The hormone levels are needed to prevent ovulation. Rifampin can also lower the effectiveness the transdermal birth control patch (Ortho Evra) and the vaginal ring (NuvaRing), so a different form of birth control should be used with these products, too. For these women, a nonhormonal method of birth control - for example, the diaphragm, copper IUD or condom, is recommended. Luckily, rifampin is an anti-tuberculosis drug that is not commonly used.

A 2002 study from the Journal of the American Academy of Dermatology states that pharmacokinetic evidence demonstrates that levels of oral contraceptive steroids are unchanged with combined administration of antibiotics, including: ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline.

A few other drugs may also affect birth control reliability. The antifungal medicine griseofulvin may lead to lower levels of birth control hormones and reduce the effectiveness of birth control pills. Certain seizures drugs, for example the anticonvulsant medications such as carbamazepine (Tegretol), phenytoin (Dilantin), primidone (Mysoline), and phenobarbital can also lower the effectiveness of combined birth control pills. Some HIV medications may also affect birth control effectiveness. Two small studies suggest that St. John's wort can induce liver enzymes, which may increase birth control pill metabolism and reduce therapeutic efficacy.

Even with study data, the association between antibiotic use and combined oral contraceptive (COC) failure is still controversial. Large clinical trials have not been completed, but many individual studies have been evaluated. Other antibiotics have not been shown in studies to make the pill less effective; however, some prescribers may still recommend that you use an added method of birth control (condom) to your hormonal method during and for one week after antibiotic treatment.

Always have your pharmacist run a drug interaction screen any time you start or stop a medication. Remember, birth control pills fail at least 1% of the time in perfect conditions, and up to 8% of the time with typical use, so taking your pill or faithfully using other reliable contraceptive methods are the key to pregnancy prevention.

See Planned Parenthood for more information.

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