 [ Symptoms ] does bactrim interfere with or reduce the effectiveness of yaz birth control to prevent pregnancy [ Disease ] your best bet for a good answer to this question is to consult your pharmacist that said we usually tell women taking oral birth control pills to use secondary birth control such as a condom when taking any antibiotic such as bactrim because some antibiotics may reduce the effectiveness of birth control pills bottom line if you do not know for sure if a particular drug is interfering with your birth control pills always use a back up solution hope this helps