Do antibiotics affect the pill?

This is one of the most common misconceptions about the oral contraceptive pill.
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August 21, 2023
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There's a lot we know about the combined oral contraceptive pill (a.k.a the pill). It's used to prevent pregnancy and help manage the symptoms of painful, irregular periods, it stops the process of ovulation in its tracks by preventing a woman’s ovaries from releasing an egg each month, and it thickens the fluid around your cervix to stop sperm from entering the body.

But there are also many myths surrounding this wonder medication, one of them being the notion that antibiotics impact its effectiveness.

So, where did this idea come from? Are there any types of antibiotics that can actually interact with the pill? And are there any other types of medication we should watch out for when on the pill?

Where the rumours began

Like all good rumours, the source of this one is hard to pin down. Fertility and IVF specialist Dr Vamsee Thalluri explains that new studies have debunked old ideas about the impacts of antibiotics on the pill.

“When I was going through medical school we were taught that if a woman’s on antibiotics you should assume the pill isn’t working,” he said.

“However, in the last few years at least a lot of new data has revealed that all antibiotics (except for a select few) don’t affect the pill at all."

“These days, it’s widely accepted that it’s only a select few types of antibiotics that impact the efficacy of the pill.

And it’s not just Dr Thalluri: other medical experts back this up, saying there are very few antibiotics that actually make an impact on the oral contraceptive pill [1].

So, why hasn’t this myth been debunked once and for all?

The confusion that exists between oral contraceptives and antibiotics is nothing new — in a recent study, nearly 30% of respondents claimed they were aware of antibiotics having an impact on the effectiveness of the pill [2].

In many cases, this confusion stems from outdated studies and data used throughout the medical profession.

“For most GPs, the medical software they use when writing up patient notes will automatically prompt an alert when they go to prescribe antibiotics to a patient that is on the pill,” says Dr Thalluri. “So even though the studies have shown that it’s safe to take both at the same time, these alerts are still coming up in the system.”

How do antibiotics work?

Antibiotics are processed by our liver and kidney. In some cases, they can cause the liver to work faster, hyper-process the pill, and reduce the amount of medication that remains in our bloodstream. With less medication, the chances of ovulation and potentially even pregnancy can increase.

And what do the experts have to say about the link between antibiotics and birth control pills? A study published in the Journal of the American Academy of Dermatology revealed that ‘plasma levels of oral contraceptive steroids’ remain ‘unchanged’ when taking most types of antibiotics, including [3]:

  • Ampicillin
  • Ciprofloxacin
  • Clarithromycin
  • Doxycycline
  • Metronidazole
  • Ofloxacin
  • Roxithromycin
  • Temafloxacin
  • Tetracycline

For women taking antibiotics while on the pill, Dr Vamsee notes that in most cases there is no need to take extra precautions (although it’s wise to speak with your GP to find out what this medication means for your specific situation).

Are there any types of antibiotics we should be wary of?

Although in most cases taking broad-spectrum antibiotics while on the pill isn’t a problem, there are certain types of medication to look out for.

The strain of antibiotics known as rifampin, in particular, has been noted to make the contraceptive pill less effective [1]. Planned Parenthood has echoed these remarks, noting that the antibiotic rifampin (also known as Rifadin and Rimactane) can, in some cases, lower the effectiveness of some types of hormonal contraception, including the pill, patch, and ring.

Another recent study published in the Canadian Journal of Infectious Diseases reinforces this, stating that oral contraceptives cannot be relied upon for birth control while taking rifampin [4].

Why is this the case?

This type of antibiotic boosts the number of enzymes in your body, which impact the effectiveness of the hormones contained in the pill.

But Dr Thalluri is quick to point out that these are not commonly prescribed antibiotics and are typically used in the treatment of tuberculosis, which isn't particularly common in Australia.

“It’s really the only type of antibiotics that can have a major impact on the liver enzymes, leading to an increased breakdown of the pill that can make this contraception less effective,” he said.

So, what can you do if you’re worried about taking these types of antibiotics while on the pill?

  • Double-up your contraception during and 7 days after your antibiotics course, such as using condoms
  • Consider using a different method of contraception entirely
  • Speak with your doctor to assess whether it’s a good idea to change the way you’re taking your oral contraceptive during this time (such as increasing your dosage)

Is it safe to take antibiotics and the pill at the same time?

In most cases, antibiotics won’t have an impact on the effectiveness of the pill and according to Dr Vamsee, "it’s completely safe to use both at the same time, but if you want to use additional contraception as a precaution that’s also safe as well".

Truth is, it's more likely that things like forgetting to take your contraception entirely will be what impacts you.

But if you are taking both antibiotics and the pill at the same time, keep in mind that:

  • If you’ve been vomiting or have diarrhoea while on antibiotics, it’s possible that you might not be absorbing the pill correctly. In this case, use backup birth control to protect yourself from the possibility of ovulation or pregnancy.
  • As a general rule, if you’ve vomited within 2 hours of taking the pill, it’s wise to use an additional method of contraception for the next 7 days.
  • It’s always a good idea to speak with your doctor to ensure you received health advice tailored to your unique situation.

Are there any other medications that can interfere with the pill?

Taking multiple medications at the same time can reduce the effectiveness of each. Although the majority of antibiotics don't interfere with hormonal contraceptives, there are other drug interactions to consider.

These include enzyme-inducing drugs that can speed up the body’s processing of some contraceptive hormones, thereby reducing the effectiveness of this method of contraception:

  • Some medications used to treat epilepsy (such as anti-epileptic drugs)
  • Some antiretroviral drugs used to treat HIV
  • The herbal remedy, St John’s Wort

If you’re concerned or have questions about the medication you’re taking, make sure to speak with your GP to find out what course of action is best for your situation.

Is the contraceptive pill right for me?

The pill can be an excellent choice for women who are looking for a simple, safe, and highly effective contraceptive method. If that's your case, you may want to consider Kin's pill subscription.

A Kin membership includes free and fast delivery of your contraception to your door 2 weeks before you run out (or earlier if you prefer), plus personalised ongoing support and handy resources on everything fertility and reproductive health — so you can easily tell fact from fiction. Simply complete an online consult with our health practitioners and they'll create a prescription plan that's right for you.

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