Which medicines affect contraception?

When you take two or more medicines at the same time, the effects of one medicine can be altered by the other(s). This is known as an interaction.

Some medicines may stop hormonal contraception working as well.

If this happens, you'll need to use extra contraception to avoid getting pregnant (such as condoms), change to a different method of contraception, or take your contraception in a different way. 

Hormonal contraceptives that can be affected by other medicines include:

• the combined pill
• the progestogen-only pill
• a patch
• a vaginal ring
• an implant

Some hormonal contraceptives may change the effect of other medicines, such as the epilepsy treatment lamotrigine and the immunosuppressant drug ciclosporin. You may be advised to change how you take the medication or to use a different method of contraception.

The patient information leaflet that comes with medicines may advise that the medicine cannot be used with certain types of contraception. This information may be different from evidence-based guidelines used by health professionals.

If you're not sure whether your contraception interacts with other medicines, speak to your GP or pharmacist.

What medicines can affect contraception?

If diarrhoea occurs as a side effect of a medicine, it could affect absorption of the combined pill or progestogen-only pill. An example of this is the weight loss drug orlistat.

Other medicines can affect the hormones in the contraceptive pill if taken at the same time. This can happen with, for example, bile acid sequestrant drugs, such as cholestyramine.

There are certain types of medicine that can increase the enzymes in your body. This is known as being "enzyme-inducing". This can affect hormonal contraception, including:

• the pill
• the implant
• the patch
• the vaginal ring

Enzyme-inducing medicines speed up the processing of some contraceptive hormones and therefore reduce the levels of these hormones in your bloodstream.

This makes the contraceptive less effective. Enzyme-inducing drugs that can affect hormonal contraception include:

• rifampicin-like antibiotics (see Will antibiotics stop my contraception working? for more information)
• some drugs used to treat epilepsy
• some antiretroviral drugs used to treat HIV
• St John's Wort (a herbal remedy)

Contraception methods that aren't affected by enzyme-inducing drugs include:

• the progestogen-only injection
• an intrauterine device (IUD)
• an intrauterine system (IUS)

If you need to start taking another medicine while you're using hormonal contraception, make sure your GP or pharmacist knows that you are using this type of contraception. They can advise you on whether the other medicine will make your contraception less effective.
 

Your GP or nurse may advise you to use an alternative or additional form of contraception while taking another medicine.

If you become pregnant while taking hormonal contraception, it will not usually affect your health or that of your baby. But you should tell your GP if you think you may be pregnant.

If you are using the IUS or IUD, you will need an ultrasound scan to rule out an ectopic pregnancy.