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Yoxly Awesome Contributors

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Medically Reviewed by:

Dr Danae Maragouthakis

When it comes to birth control, the contraceptive pill remains one of the most popular choices among women for its ease of use and high efficacy. The contraceptive pill is 99% effective at preventing pregnancy with correct and consistent use. However, there are a few things that may lower this effectiveness.

Rumours have circulated for years that antibiotics can render the pill ineffective, leaving women worried and confused about their contraceptive choices. In this blog, we'll reveal the truth behind this issue, explore different types of contraceptive pills, address antibiotic concerns, and shed light on other factors that can impact the pill's effectiveness.

Overview of contraceptive pill varieties: Combined vs. progestogen-only

Before we dive into antibiotics and their effect on contraception, let's clarify the two main types of contraceptive pills. 

  1. Combined pills: The combined contraceptive pill contains two key hormones: oestrogen and progestogen. It primarily works by suppressing the release of an egg from the ovary (a.k.a. ovulation). Additional effects include thickening the cervical mucus, which hinders sperm movement, and changing the womb (i.e. uterine) lining to make it less receptive to pregnancy.

    The combined pill is typically taken for 21 days in a row, followed by a 7-day break during which bleeding, similar to a period, occurs. If you don’t want the hassle of having a monthly period, it is still safe and effective to continue taking the pill and skip the 7-day break, but talk with your doctor first about how to do this correctly.
  1. Progestogen-only pills: The progestogen-only pill, often called the mini-pill, contains a synthetic form of the hormone progestogen. This pill works by thickening the cervical mucus, which acts as a barrier, making it more challenging for sperm to reach and fertilise an egg. In some cases, the progestogen-only pill may also suppress ovulation and alter the womb's lining.

 Unlike the combined pill, the progestogen-only pill doesn’t incorporate a 7-day break and may stop menstrual bleeding altogether while taking it. While both these pills are highly effective at preventing pregnancy, it's important to remember they do not protect against sexually transmitted infections (STIs). This means barrier methods, such as condoms or dental dams, are still necessary to protect yourself from STIs when engaging in sexual activity. If you are worried that you might have contracted an STI, consider getting one of Yoxly’s at-home STI test kits to quickly and easily rule out infections. 

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Do antibiotics reduce the effectiveness of birth control pills?

Fortunately, the widespread concern that antibiotics reduce the effectiveness of contraceptive pills is largely unfounded. The vast majority of antibiotics work by targeting bacterial infections in the body; they do notinterfere with hormonal contraception, and they do not increase your chances of getting pregnant. Phew! 

Examples of such antibiotics include:

  • Trimethoprim and nitrofurantoin: Often prescribed for urinary tract infections (UTI). 
  • Amoxicillin: Commonly used for chest infections.
  • Flucloxacillin: Typically given for skin infections.
  • Co-amoxiclav: Used for a range of bacterial infections.
  • Phenoxymethylpenicillin: Frequently prescribed for tonsillitis.
  • Metronidazole: Used for various infections, including tooth infections and bacterial vaginosis.

The Faculty of Sexual and Reproductive Healthcare (FSRH) states that additional precautions are not required when taking any of the antibiotics mentioned above. So you can go about your sexy business as usual - if you’re feeling up to it, of course!

Antibiotics that could interact with hormonal contraception

While most antibiotics do not interact with hormonal contraception, there are some exceptions to be aware of. Rifamycin antibiotics, such as rifampicin and rifabutin, are used to treat tuberculosis and are known tointeract with hormonal birth control and may compromise their effectiveness. This is because rifamycins stimulate the production of liver enzymes that break down drugs in the body, including hormonal contraceptives. As a result, the hormones found in birth control pills are metabolised much faster, reducing the concentration of contraceptive hormones in the bloodstream and potentially rendering them ineffective. According to one study, these enzyme-inducing antibiotics were associated with thirteen times more reports of unintended pregnancies!

The FSRH recommend that women using hormonal birth control in conjunction with rifamycin antibiotics should be cautious and use an additional form of contraception not affected by these drugs. This includes condoms (often ideal for short-term use of rifamycin antibiotics), intrauterine devices (IUDs) or hormone injections (which may be more desirable for people taking these antibiotics long-term). Continuing these additional contraceptive measures for 28 days after stopping rifamycin is often recommended, as the potential drug interaction may persist.

Other factors affecting contraceptive pill effectiveness

While antibiotics are not typically the culprit behind contraceptive failures, several other factors can reduce the pill's effectiveness.

  • Vomiting or diarrhoea: If you experience vomiting or diarrhoea within a few hours of taking your pill, there's a risk that your body may not fully absorb the medication. This can affect the pill's ability to prevent pregnancy. If this happens, take another pill as soon as possible and your next pill at your normal time. If diarrhoea or vomiting continues, it is best to assume you are not protected.
  • Missed or late pills: Consistency is key! Contraceptive pills should be taken at the same time every day. Missing a pill or taking it significantly later than usual can leave gaps in hormone coverage, increasing the risk of unintended pregnancy. Some pills have a more lenient time window than others, so it's crucial to read the instructions accompanying your specific pill and follow them diligently.
  • Interactions with other medications:Certain medications can interfere with the metabolism of hormones in the body, similar to rifamycin antibiotics. These include some anti-epileptic drugs, some HIV antiretroviral drugs, and an herbal supplement called St John’s wort, which some women may take to ease premenstrual symptoms. 

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The idea that antibiotics universally interfere with contraceptive pills is largely a misconception. The vast majority of antibiotics do not affect the efficacy of hormonal contraception, so there is no need to worry about unintended pregnancies if you are prescribed any of the examples listed above.

However, rifamycin antibiotics have been found to reduce the effectiveness of birth control pills by speeding up the breakdown of hormones in the liver. If you are prescribed this type of antibiotic, to be on the safe side, it is wise to use additional contraceptive methods to prevent pregnancy. Factors like vomiting, diarrhoea, missed pills, and interactions with other medications can also impact the pill's effectiveness. 

Ultimately, one of the biggest takeaway points is that you should discuss any new medication you are prescribed with your healthcare provider to ensure no interactions with your birth control. If in doubt, using condoms as an additional measure can provide extra peace of mind.

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Yoxly's Awesome Contributors (YACs) are a diverse group of individuals who are passionate about public health, and committed to furthering our mission. Yoxly provides a platform where a variety of sexual health topics (some more awkward than others!) can be explored, in an informative and non-judgmental way. If you'd like to become one of Yoxly's Awesome Contributors, contact us!