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pill-and-antibiotics

Can antibiotics affect the contraceptive pill?

If you are prescribed a standard antibiotic for a minor problem, there's generally no need to worry about your hormonal contraceptive pill. Most broad-spectrum antibiotics will have no effect on either the progestogen-only or the combined contraceptive pill.

The exception to this is when antibiotics cause you to vomit or have severe diarrhoea while taking the pill, when you will need to refer back to the pill's patient information leaflet for more instructions.

However, there are two specific antibiotics which have been proven to affect the pill (and other types of hormonal contraception).

Which antibiotics affect the pill?

The two antibiotics that have been consistently proven to affect the pill are rifampicin and rifabutin. These two antibiotics are relatively rarely prescribed, as they are used in the treatment and prevention of uncommon diseases, such as tuberculosis, meningitis and MRSA.

How do they affect the pill?

Both of these antibiotics are considered "enzyme-inducing" medicines, meaning they increase the enzyme levels in your body.

Enzymes in your body are responsible for controlling chemical reactions. When these antibiotics raise your enzyme levels, this speeds up the way your body processes contraceptive hormones. This leads to lower levels of the contraceptive hormones oestrogen and progestogen in your blood, which makes it easier for you to get pregnant.

For how long do these antibiotics affect the pill?

These antibiotics will affect the pill for as long as you are taking them and for around a month afterwards. Your doctor’s advice on how to manage the interaction between the antibiotics and your contraceptive pill will depend on the length of the course of antibiotics you are prescribed.

If you are prescribed a short course of rifampicin or rifabutin (defined as less than two months), you will need to use an extra non-hormonal form of contraception while taking the antibiotic and for a month after finishing the course. Examples of non-hormonal contraception include male and female condoms and the diaphragm. Your doctor may also advise you to make a change in your pill cycle, such as skipping your usual "pill-free" week.

On the other hand, if you are prescribed a course of antibiotics that will last two months or longer, your doctor may advise you to change to another form of hormonal contraception that isn't affected. This could be the IUD, IUS or the progestogen injection. You will need to keep using this alternative contraception for a minimum of one month after finishing the antibiotics, but can switch back to your pill afterwards.

Do antibiotics affect other forms of hormonal contraceptive?

Yes. These same two antibiotics can also affect:

  • the contraceptive implant
  • the contraceptive patch
  • the vaginal ring

By lowering the levels of oestrogen and progestogen in the blood, these two antibiotics render the above forms of contraception far less effective. If you are using one of these forms of contraception and are prescribed one of the enzyme-inducing antibiotics, you should discuss this interaction with your doctor. As with the contraceptive pill, your doctor may recommend that you use extra contraception or switch to a different type while taking the antibiotics.

The contraceptives that are not affected by these two antibiotics are: the copper IUD, the IUS, the diaphragm, both male and female condoms and the progestogen injection.

Can other drugs affect my hormonal contraception?

Rifampicin and rifabutin are the only antibiotics that are "enzyme-inducing", but certain other medications are also "enzyme-inducing". These include:

  • St John's Wort (a herbal remedy for anxiety)
  • certain epilepsy medications
  • certain HIV medications

You must always inform your doctor of anything you take regularly or of any contraception method you use when you are being prescribed a new medication. This is the easiest way to avoid interactions between drugs.

Sources:

http://www.nhs.uk/Conditions/contraception-guide/Pages/antibiotics-contraception.aspx
http://www.nps.org.au/medicines/infections-and-infestations/antibiotics/for-individuals/how-do-i-take-my-antibiotics/antibiotics-and-contraceptives

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