Q: I have a patient on birth control who is in need of an oral antibiotic. I heard something about antibiotics neutralizing the effect of the birth control pill. Anything to this?

A: Scientifically speaking, the answer is no, says optometrist and registered pharmacist Bruce Onofrey. Current scientific evidence finds that oral antibiotics dont make birth control pills less effective, he says. (One exception: rifampin, an antibiotic often prescribed for patients with tuberculosis, not ocular infection.)

Then again, Dr. Onofrey says, you have to look at this question from two perspectives: evidence-based medicine and medicolegal.
From an evidence-based medicine perspective, theres no proof that commonly prescribed oral antibiotics lessen the effectiveness of oral contraceptives.1,2 But, from a medicolegal perspective . . . well, thats a whole different story.

From the medicolegal side, people have won lawsuits in which they claimed that the antibiotic they took caused a loss in effectiveness of their birth control and they became pregnant, Dr. Onofrey says. Such legal precedent was derived from anecdotal reports and long-outdated studies that suggested a connection.

But, the warning persists. Many antibiotics still list a drug interaction in the prescribing information.
I was taught this as a pharmacist, Dr. Onofrey says. Its still in my pharmacy board books when I take my recertification exam. It just keeps popping its head up.

Many antibiotics still list an interaction (now outdated) with oral contraceptics.

Why wont this connection go away? Just as there are no large-scale scientific studies to prove that there is a connection, there are no large-scale scientific studies to prove that there isnt a connection either, says Jill Autry, also an O.D. and registered pharmacist.

Proving that there is no connection would be hard to do, she says.
For one, oral contraceptives are not 100% effective; the failure rate may range from 1% to 3%.1 So, it would be impossible to distinguish which patients became pregnant because of an antibiotic interaction and which simply experienced the normal failure rate of birth control, Dr. Autry says. (Then again, since both drugs are prescribed for so many women, youd expect a much higher rate of contraceptive failure in women taking both drugs if there is a true drug interaction, she says.)

For another, the clinical studies to date have been too small to detect such a rare interaction. Even with thousands of participants, the incidence of an interaction might not even be statistically significant, Dr. Autry says. In other words, such an interaction might still fall within the normal failure rate of birth control.

Q: So, what do I tell my patient?
I dont want to add to the hype, but I also dont want to be sued.

For what its worth, both Dr. Onofrey and Dr. Autry rarely mention the possibility when they prescribe an oral antibiotic.

Having a patient on birth control has never prevented me from treating her with an antibiotic, Dr. Onofrey says. (He points out that although patients have won lawsuits based on this precedent, at least one doctor has prevailed in such a case.)

However, if you want some shred of medicolegal protection, he says, tell both sides of the story and the leave the decision up to the patient. You could say there is some belief that antibiotics occasionally make birth control less effective, although you could also say that the scientific evidence doesnt support that, Dr. Onofrey says. But, if its important for the patient to avoid getting pregnant, then she may want to practice alternative birth control methods during the treatment period.


1. DeRossi SS, Hersh EV. Antibiotics and oral contraceptives. Dent Clin North Am 2002 Oct;46(4):653-64. Review.

2. Archer JS, Archer DF. Oral contraceptive efficacy and antibiotic interaction: a myth debunked. J Am Acad Dermatol 2002 Jun;46(6):917-23. Review.

Vol. No: 145:05Issue: 5/15/2008