It depends on which antibiotic you were given. Z-pak, Zithromax do NOT cancel out your BC. Penicillin, amoxicillin do mess with your BC. Those 2 are just off the top of my head. If you have the name of your antibiotic or any other meds you have questions about, feel free to message me. Did you remind your doctor that you are on Birth control pills?? Just because they have your file right in their hand, does not mean they know everything on it right off the top of their head. Its sad to say, but the medical field has become so rushed, that doctors just don''t have the time to spend with each of their patients that they would really like to.