Wow I'm kind of shocked your gyn told you it might be affected, then again she just may not know better.

Antibiotics, such as penicillins (ampicillin, amoxicillin), tetracyclines, or metronidazole (Flagyl), do not change the effectiveness of birth control pills.

The ones you should watch out for are:

* St. John's wort.
* Certain antibiotics such as rifampin (Rifadin) and griseofulvin (Fulvicin).
* Anticonvulsants, such as carbamazepine (Tegretol), phenobarbital, phenytoin (Dilantin), and primidone (Mysoline).
* Narcolepsy medications, such as modafinil (Provigil).
* Antiretroviral protease inhibitors used to treat HIV, such as Ritonavir.