oral contraceptives

Should women using oral contraceptives to prevent pregnancy be warned to take extra precautions if they need to take an antibiotic? There is surprisingly little agreement on this in the medical community, although pharmacists and gynecologists accept that rifampin can affect birth control pills (Simmons et al, BJOG, June 2018). This seems like a simple question, but it doesn’t have a simple answer. Here is one woman’s unsettling experience:

Does Penicillin Interact with Oral Contraceptives?

Q. I went to urgent care for a bad sore throat last night and was diagnosed with strep. They very carefully noted relationship status and birth control (Tri-Previfem) in my freshly created record. I was prescribed penicillin for ten days. At no point was I told the antibiotic might interact with my birth control.

I wondered about that and started investigating. Google was less than helpful. When I called my pharmacy, a staff member asked the pharmacist on my behalf. They told me it would interact, and my birth control would be ineffective. I asked how long this would last and was told until 24 hours after the last dose of antibiotics.

I am concerned that I had to actively hunt for an answer and further concerned that I haven’t really found one. If I skipped 10 days of the pill, it would not start working on day 11. Do antibiotics make it different?

Questions Remain About Antibiotics Interacting with Oral Contraceptives:

A. We were shocked to discover that this question has not been fully resolved. Even though oral contraceptives (OCs) have been used for decades, there is no consensus about whether antibiotics reduce their effectiveness (Hoffmann et al, Reproductive Health, online, May 14, 2015).

The authors of this review conclude:

“Clinicians are encouraged to advise female patients on the use of additional measures of birth control during and up to one week after antibiotic therapy.”

We have heard from women who became pregnant while taking an antibiotic with their OC. Although most women may not have such stark evidence of an interaction between their oral contraceptives and antibiotics, doctors cannot tell which women might be vulnerable. Consequently, we think it would be prudent to take precautions. We suggest you use a barrier contraceptive method during your treatment and for a week after finishing your course of penicillin.

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  1. Dolores J

    Does this precaution hold true for all antibiotics or just penicillin?

    • Terry Graedon

      It holds for all antibiotics, although the advice is somewhat controversial (as we discussed). It is not at all controversial for rifamycin and rifampin. They clearly and definitely do interact with oral contraceptives to render them less effective.

  2. Caroline

    It has been many years since I was on oral contraceptives for birth control but I was always told to use an additional form of BC for the rest of that cycle when I needed antibiotics.

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