emergency contraception and antibiotics

Last reviewed 01/2018

There is no requirement to increase the dose for emergency contraception if the patient is taking antibiotics that are not enzyme inducers.

If hormonal methods of emergency contraception and the patient is currently taking enzyme inducing anti-epileptic medication (e.g. phenytoin) then the levonorgestrel dose should be:

  • 1.5 mg taken immediately followed 12 hours later by a further 1.5mg dose - note that this is an unlicensed dose and the woman should be advised accordingly (1,2)

Guidance has been given regarding the use of emergency contraception and enzyme inducing drugs (3)

  • women who request oral EC while using enzyme-inducing drugs or within 28 days of stopping them, should be advised to take a total of 3 mg LNG (two 1.5 mg tablets) as a single dose as soon as possible and within 120 hours of unprotected sexual intercourse (UPSI) (use of LNG >72 hours after UPSI and double dose are outside the product licence)

  • Ulipristal acetate (UPA) is not advised in women using enzyme-inducing drugs or who have taken them within the last 28 days

  • women should be advised that UPA has the potential to reduce the efficacy of hormonal contraception. Additional precautions are advised for 14 days after taking UPA (9 days if using or starting the POP, 16 days for Qlaira®)

  • Advice for women using drugs that may reduce contraceptive efficacy
    • Women using drugs that affect gastric pH (e.g. antacids, H2 antagonists and proton pump inhibitors) and who require EC should be offered a Cu-IUD or LNG as the efficacy of UPA may be reduced.

Drugs which induce liver enzymes include:

  • antiepileptic - Carbamazepine, Eslicarbazepine, Oxcarbazepine, Phenytoin, Phenobarbital
  • antibiotics - Rifabutin, Rifampicin
  • antiretroviral
    • protease inhibitors - Ritonavir, Ritonavir-boosted atazanavir, darunavir, fosamprenavir, lopinavir,
    • non-nucleoside reverse transcriptase inhibitors - Efavirenz, Nevirapine
  • Herbal - St Johns Wort (3)

Women who are using enzyme inducing drugs and are in need of EC should be informed that a copper intrauterine device (Cu-IUD) is the most effective method of EC (3).


  1. BNF 7.3.1
  2. NICE (October 2004).The epilepsies: the diagnosis and management of the epilepsies in adults and children in primary and secondary care.
  3. Faculty of Sexual & Reproductive Healthcare Clinical Guidance. Drug Interactions with Hormonal Contraception.Clinical Effectiveness Unit; January 2011.