Antibiotics and contraception

Broad-spectrum antibiotics are no longer thought to reduce the efficacy of combined oral contraceptives and contraceptive patches or rings.
The Faculty of Sexual and Reproductive Healthcare Clinical Guidance: Drug Interactions with Hormonal Contraception states that additional contraceptive precautions are no longer necessary when antibacterials that do not induce liver enzymes are taken with combined oral contraceptives, unless diarrhoea or vomiting occurs. Also, no additional contraceptive precautions are required when contraceptive patches or vaginal rings are used with antibacterials that do not induce liver enzymes.
The antibiotics included in this guidance do not induce liver enzymes therefore additional contraceptive precautions are not required for patients taking short courses of these drugs unless diarrhoea or vomiting occurs.