The effectiveness of “combined oral contraceptives”, “progestogen-only” oral contraceptives, contraceptive patches , vaginal rings, and emergency hormonal contraception can be considerably reduced by interaction with drugs that induce hepatic (liver) enzyme activity. Some common examples include:
- Carbamazepine
- Phenytoin
- Phenobarbitone
- St John’s Wort
- Topiramate
- Rifampicin
- Griseofulvin
For short-term use of enzyme inducing drugs alongside combined oral contraceptives, it is suggested that appropriate barrier methods such as condoms are used for the duration of the treatment, and continued for 4-weeks after stopping.
For patients on long-term courses of potent enzyme inducing drugs such as Rifampicin and Rifabutin, it is recommended that an alternative method of contraception such as an IUD (intrauterine device) or coil is used instead of the combined oral contraceptive and continued for 4-weeks after stopping.
It is recommended that no additional contraceptive precautions are required when combined oral contraceptives, contraceptive patches or vaginal rings are used with antibacterials that do not induce liver enzymes, unless diarrhoea or vomiting occur.
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