Myth: Antibiotics stop combined hormonal contraception from working
Date: 01 Dec 2017
Author: Clinical Effectiveness Team
The FSRH CEU provides clarification on evidence on broad-spectrum antibiotics and whether they impact the effectiveness of CHC.
The CEU advises that additional precautions are not required when using non-enzyme inducing antibiotics with combined hormonal contraception (CHC). 1 This is following review of the evidence which revealed that most broad-spectrum antibiotics are non-enzyme inducing and therefore do not require any special precautions. 2 This advice is a change from previous guidance on the subject which advised additional precautions when taking non-enzyme inducing antibiotics with CHC. The only provision would be if the antibiotics caused vomiting or diarrhoea (i.e. vomiting within 2 hours of pill taking or experiencing severe diarrhoea). In this case, the usual additional precautions for CHC use relating to these conditions should be observed.1
On the other hand, enzyme inducing antibiotics (e.g. rifampicin and rifabutin) increase the metabolism of estrogens and progestogens, which may in turn reduce the contraceptive efficacy of CHC.1 Women using enzyme-inducing antibiotics should ideally switch to a method that is unaffected by these drugs. This includes all intrauterine contraception and the progesterone only injectable. These methods will provide effective contraception whilst women are using enzyme inducing antibiotics and should be retained to provide contraceptive cover for 28 days after stopping the enzyme-inducing medication.2 Short-term use of enzyme inducing drugs (<2 months) can be managed more flexibly than longer term use. For these women, and those who do not wish to change methods, continuing their current method with careful use of condoms (while they are on enzyme inducers and for 28 days after) may be appropriate. 2
1. Faculty of Sexual & Reproductive Healthcare.Combined Hormonal Contraception. October 2011 (Updated August 2012). Available at https://www.fsrh.org/standards-and-guidance/documents/combined-hormonal-contraception/ (Accessed 25/04/17)
2. Faculty of Sexual and Reproductive Healthcare Clinical Effectiveness Unit. Drug Interactions with Hormonal Contraception. 2017. https://www.fsrh.org/standards-and-guidance/documents/ceu-clinical-guidance-drug-interactions-with-hormonal/ [Accessed 25/04/17].