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You have probably heard that antibiotics interact with the birth control pill in a way that may cause your contraception to fail. Many women who are on the pill are worried about this, while others are simply curious.

The birth control pill's ingredients and dosages have changed over time, and research into its interactions with other drugs has advanced. Do antibiotics (still) lead to hormonal contraceptive failure? What do you need to know about how the pill combines with other drugs? 

Medical professionals used to caution pill users against relying on their contraceptive while using any type of antibiotic. You have most probably heard stories from or about women who got pregnant while they were on the pill, because they were on a course of antibiotics. This may make you wonder if you need to use an additional form of contraception, like condoms, while you are taking antibiotics. You may also wonder if there are any other drugs that cause hormonal contraceptives to fail.

The story is a little more complicated than just "using antibiotics may lead to pill failure". A lot depends on the type of pill you are on, and the rest depends on the kind of antibiotics you are prescribed. The World Health Organization can be seen as the foremost authority on which contraceptive is suitable for whom, in which circumstances. Their Medical Eligibility Criteria (MEC) are carefully crafted, and applied in countries including the US and UK with only minor adaptations to reflect the needs of local populations.

In recent years, the WHO's MEC as well as the US and UK guides have been amended, and now advise that many antibiotics can safely be used together with combined oral contraceptives (birth control pills that use two different hormones). Antibiotics that are not enzyme inducers have been shown not to disrupt the way in which the pill works. Women who are pill users, and who get an antibiotic prescription from their family doctor or any other healthcare provider, like a dentist, should always remind their doctors that they are on the pill. You can provide details on which pill you use if prompted, because some doctors do not have all of your medical records and may not be aware. Healthcare providers will have access to the full MEC, and will know which antibiotics do interact with the pill and which don't.

Enzyme inducers will require an additional form of contraception for a while. You can use condoms, or even opt to have a copper coil placed. This is, again, something that you should discuss with your doctor who will know which drugs are enzyme inducers. It is important to note that drugs that are not antibiotics can be enzyme inducers as well. Short-term use of these medications should be backed up with condom use for 28 days, or one whole cycle of the pill, to prevent an unwanted pregnancy.

What happens if you had "unprotected sex" (pill use along with enzyme inducing drugs, forgetting to use the condom)?

You should be aware that the morning after pill uses much of the same hormones that are also used in regular birth control pills. Therefore, hormonal emergency contraceptives may not be effective. Talk to your doctor as soon as you can about what happened, because you do have another option. Most women are not aware that the copper coil or intrauterine device can serve as an emergency contraceptive. A final thing you want to be aware of is that some drugs are affected by hormonal contraceptives too, so the story can work both ways. If you require medications for any reason, you want to know if using the pill makes them less effective or completely ineffective.

Again, this is something that your healthcare provider should know about checking how these interactions work is a pretty specialized activity. Your responsibility ends with asking questions, receiving satisfying answers, and informing your healthcare provider about all the drugs that you take. This includes recreational drugs and herbal medications, which can definitely interaction with other medications. In the source list below, I've shared a document that goes into the way in which hormonal contraceptives can interact with other drugs. The guide is very much aimed at healthcare providers, may be interesting to you as a pill user because it contains names of medications you want to apply special caution with.

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