Does morning after pill take effect even on antibiotics?

Yes: Plan B is effective even if you are on antibiotics. Remember, though, that Plan B should not be your primary form of contraception. It is an emergency contraceptive. If you are routinely sexually active, decide on a different form of reliable birth control if you are not ready to be a parent (or if already a parent, have additional kids).

Some decrease effect: Specific antibiotics called microsomal inducers can reduce the effect of plan B These medications increase the breakdown of plan B in the liver and hence reduce its effectivity . Ampicillin , cotrimoxazole , rifampin, tetracycline and Clarithromycin specifically reduce the effect.