Rifampicin and the contraceptive pill: reduced effectiveness explained

Rifampicin is an antibiotic best known as part of the treatment of tuberculosis. The NHS says the main treatment for TB is antibiotics, usually for at least 6 months, and 3 to 6 months for latent TB without symptoms. The NHS page does not name the individual antibiotics, so this page relies on the BNF entry for rifampicin itself.

One BNF entry for rifampicin refers to the enzyme inducing drug, which is the grouping that the wider interaction guidance uses. The BNF list for rifampicin is long, which is why contraception is only one among many topics for people taking it.

Rifampicin is the name used in the BNF and across UK services. Some websites use the US name, rifampin, which is why this guide refers to both.

In the BNF interaction list for rifampicin, the entry for combined hormonal contraceptives states that rifampicin is predicted to decrease the efficacy of combined hormonal contraceptives, and it directs readers to CoSRH guidance in the contraceptives interactions section. The severity is severe and the evidence type is study.

The list also names individual hormones. For desogestrel, the entry states that rifampicin is predicted to decrease the efficacy of desogestrel, with severity severe and evidence theoretical. A related entry for cyproterone with ethinylestradiol advises using alternative methods during treatment and for 28 days after the enzyme inducing drug is stopped.

The BNF does not reproduce the detail in its interaction entry, so the exact advice, including how long extra protection is needed, sits in the CoSRH guidance that it points to.

The NHS combined pill page says that if used correctly it is more than 99% effective, and that if not used correctly it is 91% effective, so that about 9 in 100 women will get pregnant in a year. It says some medicines and herbal remedies can affect how the pill works, so that it may not work properly to stop you getting pregnant. It advises asking a doctor or pharmacist for advice before taking the pill if you take medicine for TB, epilepsy or HIV, and also if you take griseofulvin, lamotrigine or St John's wort. It adds that you may need another type of contraception.

The NHS carbamazepine page similarly lists some types of hormonal contraception, such as the contraceptive pill, patch or implant, among things that may not mix well with it. The theme is consistent: enzyme-inducing medicines are a recognised reason to review contraception.

If you are about to start rifampicin, tell the prescriber that you use hormonal contraception, and ask for a contraception review at the same time. Options a sexual health clinic or GP may discuss are method changes or additional barrier protection. The BNF entry points to the faculty guidance, so the exact plan, including how long it lasts after the antibiotic stops, comes from that source.

Do not stop rifampicin because of contraception concerns, and do not stop taking the pill without a plan. If you have had unprotected sex, or are unsure whether protection has been affected, ask a pharmacist or sexual health service about emergency contraception.

• Say that you use hormonal contraception when rifampicin is prescribed.

• Ask for advice on another method or extra protection.

• Ask how long extra precautions are needed after the course ends.

• Seek emergency contraception advice promptly after unprotected sex.

Within the NHS, GP practices, sexual health clinics and community pharmacists can review contraception, and the TB service that prescribes rifampicin can flag the issue. Private clinicians and pharmacies use the same guidance, so the same question applies: tell them which hormonal method you use and which antibiotics you take.

This site has a separate guide to enzyme-inducing medicines, contraception and anticoagulants, and to antibiotics and the contraceptive pill, which contrasts rifampicin with ordinary antibiotics.