Ciprofloxacin bottle on pharmacy shelf

Answer

Most antibiotics are not thought to interact significantly with birth control pills.

There are certain antibiotics that are exceptions to this though, including the "rifamycin" family of antibiotics.

These antibiotics can significantly increase how fast we metabolize the hormones in birth control pills, decreasing effectiveness.

When it comes to Cipro (ciprofloxacin), most available data indicates that it will not affect your birth control pill and should not put you at an increased risk of pregnancy.

However, a few studies have noted that a very small percentage of individuals may experience significant drops in hormone concentrations with antibiotics for reasons not entirely understood.

As the consequences of unplanned pregnancy are great, it generally is a good idea to use back-up contraception, such as condoms, while taking antibiotics like Cipro.

We discuss the details regarding this below.


How Can Cipro Affect Birth Control Pills?

As we know, antibiotics kill bacteria. Unfortunately, they also get rid of some of the "normal bacterial flora" in our gastrointestinal tract. The bacteria in our gut is very important for many bodily functions, including in the metabolism of hormones from birth control pills.

The bacteria in our gut is responsible for what is known as estrogen enterohepatic recirculation. In simple terms:

  • The estrogen from birth control pills is metabolized in the liver.
  • Some of this metabolized estrogen is released back into the gut.
  • The bacteria in our gut turn the metabolized estrogen back into active estrogen, which we then re-absorb.

If we reduce the bacteria in our gut, theoretically, there will be less estrogen to absorb, decreasing concentrations, and potentially decreasing how well birth control works.

Nevertheless, most studies on the matter state that the amount of estrogen lost from a reduction from GI bacteria is minimal and will not significantly affect birth control pills.


Recommendations

While most studies show that Cipro will not affect your birth control, the concern comes from data showing that a very small number of individuals do appear to be affected. Per one study:

"Pharmacokinetic studies of other antibiotics have not shown any systematic interaction between antibiotics and OC [oral contraceptive] steroids. However, individual patients do show large decreases in the plasma concentrations of ethinyl estradiol when they take certain other antibiotics, notably tetracycline and penicillin derivatives. Because it is not possible to identify these women in advance, a cautious approach is advised."

In total, the risk of having your birth control pill not work as well on Cipro is low.

However, to be safe, many healthcare professionals will recommend that you use back-up contraception. It is an easy task compared to what would come with an unintentional pregnancy.

In terms of how long to use back-up birth control, the most common recommendation is for the length of time you take the antibiotic and for 7 days after you finish your antibiotic.

This allows time for the bacteria in your gut to "re-grow" and for hormone concentrations from the birth control pills to return to a normal level (if they were affected).


Summary

  • Certain antibiotics, such as 'rifamycin' antibiotics, are well-known to decrease birth control concentrations.
  • Cipro (ciprofloxacin) is not a rifamycin antibiotic, and isn't thought to reduce the effectiveness of birth control for most individuals.
  • Nevertheless, a small percentage of people may be affected and therefore, as a safety precaution, the use of back-up contraception may be prudent.

  • References
    1. Drug interactions between oral contraceptives and antibiotics. ScienceDirect
    2. Updated Clinical Guideline Published: Drug Interaction with Hormonal Contraception. FSRH