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Do Antibiotics Interact with Oral Contraceptives?

An unplanned pregnancy is life-changing. Why aren't women warned that antibiotics may interact with oral contraceptives? When 1+1=0 and 3!

Here’s a riddle for you: When does 1+1= 0 and 3 simultaneously? The answer: When a woman takes antibiotics together with birth control pills. That’s because the antibiotics can reduce the effectiveness of the BC pills down to 0 and that can lead to an unexpected pregnancy. The bottom line, then, is that drugs which interact with oral contraceptives can simultaneously lead to ineffectiveness (1+1=0) and a baby (1+1=3). 

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.

Medicine and Pharmacy Perplexed by Drug Interactions:

Drug interactions are the Achilles heel of both medicine and pharmacy. That’s because research on this complicated problem is often lacking. In addition, physicians and pharmacists rely on databases that may be inaccurate or outdated, not to mention confusing. There is no single standardized system to tell health professionals which combinations are dangerous or life threatening. Once an interaction is listed in a computerized database, it can be challenging to get it changed.

Sometimes one drug cancels out the benefits of another. Other times an interaction leads to unanticipated complications. And every once in a while, a combination of compounds can lead to a lethal outcome. 

Decades ago, I was interviewed on the Oprah Winfrey Show about drug interaction problems. I was joined by a woman who had taken an antibiotic that could interact with oral contraceptives. She had become pregnant. There had been no caution from her physician or pharmacist.

Other women have written to tell us that they too were not warned that antibiotics could interact with oral contraceptives. Here are a few examples:

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 oral contraceptives.

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! Do Antibiotics Interact 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 over 60 years, there is still no consensus about whether antibiotics reduce their effectiveness.

Here is an analysis published in CPT Pharmacometrics & Systems Pharmacology (Nov. 2018)

“Hormonal contraceptive agents (HCAs) are widely used throughout the world, and women taking HCAs are likely to take other medications. However, little is known about the clinical effect of most drug-drug interactions (DDIs) associated with HCAs.”

That’s right; after 60 years we still do not know which drugs can interact with oral contraceptives.

Another review concludes (Hoffmann et al, Reproductive Health, online, May 14, 2015):

“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.”

When Antibiotics Interact with Oral Contraceptives There ARE Consequences:

This reader did not learn about such an interaction until it was too late:

“I am pregnant and I believe it is because of an antibiotic my doctor prescribed. He says that is impossible and that I must have skipped a pill. I am extremely conscientious about my birth control pills. It makes me mad that he is treating me like an airhead.”

We certainly appreciate the outrage. No one should be treated like an “airhead” or told that an interaction like this is “impossible.” As British researchers recently noted:

“an unintended pregnancy is a life-changing event” (BMJ Evidence-Based Medicine, online Aug. 18, 2020). 

We heard from another woman:

“I am seven months pregnant although I never missed a single day of my birth control pills. But when I came down with bronchitis, the doctor prescribed an antibiotic. Neither the physician nor the pharmacist warned me about a potential interaction, and I was too sick to think about my oral contraceptive not working.

“Although my significant other and I have been together for some time, we are not married. Try to imagine the havoc this has caused in both our lives. When pregnancy occurs out of your control, you cannot begin to imagine the possible damage, the heartache and the worry. I hope that more people tell their stories, and that something can be done to warn users of oral contraceptives.”

Although most women may not have such stark evidence that antibiotics interact with oral contraceptives, doctors and pharmacists cannot tell which women might be vulnerable. We recognize that this interaction remains controversial and drug interaction databases are ambiguous.

The British researchers we cited above (BMJ Evidence-Based Medicine, online Aug. 18, 2020) conducted a study on women’s reports of their experience.

They conclude:

“Compared with control medicines, unintended pregnancies were seven times more commonly reported with antibiotics…This study provides a signal that antibacterial drugs may reduce the efficacy of hormonal contraceptives.”

They recommend that prescribers warn women that antibiotics may impair the effectiveness of their birth control pills. Women should be encouraged to use extra precautions such as barrier contraceptives while taking antibiotics and perhaps for a few weeks thereafter. We suspect that if medical practices or pharmacies had to pay child support, they would be a lot more careful about drug interaction warnings.

Do You Worry About Drug Interactions?

It’s not just antibiotics that interact with oral contraceptives. There are literally tens of thousands of potential drug interactions that impact health. Some antibiotics can make particular blood pressure medicines life threatening.

You can read about deadly drug interactions and ways to protect yourself in our book, Top Screwups Doctors Make and How to Avoid Them. There is also a chapter about pharmacy. We provide our Top 11 Tips for Preventing Dangerous Drug Interactions. Here is a link. If you click on the video you will learn why we are so passionate about this topic.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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