Antibiotics and Birth Control Pills

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Antibiotics and Birth Control Pills

Question:

Before her oral surgery, my daughter was put on antibiotics. The surgeon said this would cause her birth control pills to be ineffective. Once she is finished with the antibiotics, does she need to wait for a period of time to begin sexual activity?

Answer:

Large studies show that pregnancy rates are the same in women who take birth control pills whether or not they also take antibiotics.

However, the issue is more complicated. The answer depends on the antibiotic used and probably on the unique characteristics of the woman. At this point, we cannot predict or measure these variables.

The level of hormones in the blood of a woman using birth control pills varies substantially. This suggests wide differences in how the body processes the drug.

However, when used consistently, even today's low dose birth control pills protect against pregnancy.

It is possible, though not proven, that some women may be at risk for a drug interaction and the failure of the birth control pills to work. These women metabolize drugs more quickly.

In addition, several drugs, including the antibiotic rifampin, are cleared from the body by a process that may speed up the metabolism of birth control pills. Using these drugs may lower the pill's effectiveness.

Doctors vary in the recommendations they make for their patients based on this information. A cautions approach is to use a backup means of contraception, such as condoms, while on a short course of antibiotics. Women using drugs such as rifampin or who are on antibiotics long term may consider alternative means of contraception.

Joan Bengtson, M.D., is assistant professor of obstetrics, gynecology and reproductive biology at Harvard Medical School and a member of the Department of Obstetrics, Gynecology & Reproduction at Brigham and Women's Hospital.

Last updated:	July 20, 2009