Can antibiotics make birth control less effective?

Bottom lineFor most antibiotics, no, that's a myth: everyday antibiotics like amoxicillin and doxycycline don't reduce hormonal birth control's effectiveness. Only enzyme-inducing drugs, mainly the antibiotics rifampicin and rifabutin (plus some anti-epileptics and St John's Wort), reliably interfere, requiring backup contraception; vomiting or severe diarrhea can also stop the pill being absorbed, so follow missed-pill advice and ask a pharmacist if unsure.

For most antibiotics, no - this is a common myth. Only a specific group of medicines reliably reduces hormonal contraception's effectiveness.

The medicines that DO interfere

• Enzyme-inducing drugs, especially the antibiotics rifampicin and rifabutin (used for TB and some infections)
• Some anti-epileptic drugs and the herbal remedy St John's Wort

These speed up how your body breaks down the hormones, lowering their levels.

The common antibiotics that DON'T

Everyday antibiotics like amoxicillin, penicillin, doxycycline, and most others do not make hormonal birth control less effective. Older advice to use backup with all antibiotics has been updated.

What can still cause failure

• Vomiting or severe diarrhea (from illness, not the antibiotic itself) can stop the pill being absorbed
• Missing pills while unwell

What to do

• If prescribed rifampicin/rifabutin, use additional contraception (like condoms) during and for a while after - ask your clinician or pharmacist
• For most antibiotics, keep taking your contraception as normal
• If you vomit within 2 hours of a pill or have severe diarrhea, follow the missed-pill instructions
• When unsure, ask a pharmacist - they can check your specific medicine

See can antibiotics affect vaginal health for the related effect on infections.

Femora helps you track pills and any illness that might affect absorption.