Birth Control (Contraception) Expert Forum
Birth Control and Antibiotics
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Birth Control and Antibiotics

I've been on birth control for over a month. My doctor prescribed me 500mg azithromycin for a day, then 250mg for 4 days because I have sinus infection. On my second day of taking the antibiotic, I had unprotected sex and was very worried because I have heard antibiotics can decrease the effectiveness of birth control. I went to Walgreens and bought the emergency contraceptive Next Choice pill, and it says you can take it within 72 hours. I took it 38 hours after the unprotected sex. I take my birth control the way it says, never missing a pill. Should I still be worried and is there a possibility that the pill didn't work because I took it 38 hours after unprotected sex?
603463_tn?1220630455
Hi!
If you were my patient, I would advise you that first of all there is no good evidence to suggest that antibiotics reduce the effectiveness of the pills.  The data on the well done studies seems to indicate that the effectiveness does not change, except in the case of some unusual antibiotics such as Rifampin.  Secondly, if you are taking your birth control pills appropriately, ovulation should have been prevented this cycle.  Finally, the emergency contraceptive should be effective up to 120 hours after intercourse.  Effectiveness decreases with time, but the chance that you are pregnant is close to zero.  ANYTHING can happen, but you certainly shouldn't lie awake at night worrying!
Good luck!
Dr B
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