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Contraception - Management
Drug interactions with the combined oral contraceptive

What should I advise a woman regarding potential drug interactions with combined oral contraceptives (COCs)?

  • Liver enzyme–inducing drugs, some antibiotics, and some natural remedies, can reduce the efficacy of combined oral contraceptives (COCs).
  • COCs can alter serum concentrations of other drugs, such as lamotrigine, ciclosporin, and theophylline.

In depth

What should I advise a woman about taking combined oral contraceptives (COCs) with a liver enzyme-inducing drug?

  • Liver enzyme–inducing drugs may reduce the efficacy of combined oral contraceptives (COCs). Commonly encountered drugs include:
    • Antibiotics: rifampicin and rifabutin
    • Anticonvulsants: carbamazepine, oxcarbazepine, phenytoin, barbiturates, primidone, topiramate.
    • Antiretrovirals: particularly non-nucleoside reverse transcriptase inhibitors and ritonavir-boosted protease inhibitors. Drug interactions between certain antiretroviral agents and hormonal contraceptives could alter the safety and effectiveness of both the contraceptives and the anti-retroviral agents. For further information, see antiretrovirals.
    • Herbal remedies: St John's wort
  • If a liver enzyme–inducing drug is to be used long-term:
    • An alternative contraceptive method that is unaffected by enzyme-inducing drugs should be considered, for example, a long-acting reversible method such as s depot medroxyprogesterone, levonorgestrel-releasing intrauterine system or a copper intrauterine device (IUD).
    • If the woman wishes to use the COC as her primary contraceptive method while taking a liver enzyme–inducing drug, refer to (or consult with) a specialist. A COC regimen with at least 30 micrograms of ethinylestradiol daily should be used, and/or taking the COC without a pill-free interval — these uses are outside the terms of the product license.
    • The consistent use of condoms is recommended.
  • If a liver enzyme–inducing drug is to be used short term (e.g. 3 weeks):
    • Additional contraceptive protection (e.g. condoms) should be used while the liver enzyme–inducing drug is being taken and for at least 4 weeks after stopping it. For women using rifampicin or rifabutin, consider continuing alternative methods for up to 8 weeks after stopping it.
  • Emergency contraception should be considered if sexual intercourse has taken place while efficacy of the COC is doubtful and within the past 5 days — see the CKS topic on Contraception - emergency.

In depth

What should I advise a woman about taking a combined oral contraceptive (COC) with an antibiotic?

  • Additional contraceptive precautions are not required during or after courses of antibiotics that do not induce liver enzymes.
  • However, women should be advised about the importance of correct contraceptive practice during periods of vomiting or diarrhoea.
  • Rifampicin and rifabutin induce liver enzymes. Therefore, if the woman is taking, or needs to take, rifampicin or rifabutin at the same time as a COC, follow the advice for interactions with liver enzyme-inducing drugs.

In depth

Interactions with lamotrigine: what should be done?

  • If the woman is already receiving lamotrigine:
    • If she wishes to start a combined oral contraceptive (COC), advise her:
      • That a COC containing a minimum of 30 micrograms of ethinylestradiol should be used.
      • That seizure control may worsen.
      • That the maintenance dose of lamotrigine may need to be increased as much as two-fold, according to clinical response.
    • If she wishes to stop a COC, advise her:
      • That adverse effects associated with lamotrigine can increase.
      • That the maintenance dose of lamotrigine may need to be decreased by as much as 50%, according to clinical response.
  • If the woman is already using a COC and wishes to initiate lamotrigine:
    • The usual escalation regimen for lamotrigine is recommended.

In depth

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