Taking Fluconazole While On Birth Control: What Should You Do?

Over 10 million women in the United States are on oral contraceptives, or "birth control pills". A very common question that gets asked and just doesn't seem to get a good answer is, “Do antibiotics reduce how effective birth control is?" In this article, we examine how Diflucan (Fluconazole) affects birth control and what you can do if you need to take the two medications together.

Question

I am on the birth control (oral contraceptive) Junel and have been for several months now. My family doctor recently prescribed Fluconazole for a slight yeast infection. The fluconazole is a one time dose. I took the dose yesterday. Yesterday was also the first day of my inactive pill week. I was told that a back-up method of birth control should be used for a week while on the medication, as it could possibly affect the strength of the birth control. We always use condoms, but last night the condom failed. Should I be concerned and do I need to do anything (like take Plan B)?

Asked by Angelini On Oct 04, 2017

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Oct 04, 2017

Birth ControlThere is some controversy as to whether or not Diflucan (fluconazole) will affect birth control to the point where it is not effective in preventing pregnancy. The majority of the data available shows that fluconzole actually INCREASES the estrogen and progestin contained within birth control. This means that theoretically, taking fluconazole and Junel should not decrease the efficacy of the medication. 


Fluconazole is a known CYP3A4 (Cytochrome P450 3A4) inhibitor. CYP3A4 is a metabolizing enzyme mainly found in the liver and intestines and is the predominant enzyme that metabolizes, or breaks down the estrogen component of birth control, ethinyl estradiol. When the enzyme is inhibited (meaning it is no longer working at full strength), the concentrations of ethinyl estradiol in the body are actually increased over what they would normally would be if the enzyme wasn't inhibited. Many progestins as well follow this mechanism of metabolism.


The Prescribing Information, or Package Insert, for fluconazole shows empirical data on how it affects the hormones contained in oral contraceptives. It references 3 studies in which ethinyl estradiol and progestin concentrations were measured after giving a dose of fluconazole to a patient. 


  • ​In the first study, fluconazole was given at a dose of 50mg per day for 10 days. Both the estrogen and progestin concentrations were raised on average by 6% and 17% respectively.
  • In the second study, patients were given a 200mg dose of fluconazole.  Both the estrogen and progestin concentrations were raised on average by 38% and 25% respectively.
  • Lastly, in the third study, patients were given a once weekly dose of 3o0mg of fluconazole. Both the estrogen and progestin concentrations were raised on average by 24% and 13% respectively. 


While the above data shows an average increase in birth control hormone concentrations after fluconazole dosing, the studies did show that a small number of individuals showed a slight decrease in concentration. While study 3, referenced above, showed an average increase in concentrations, there were 3 people in that study that had a drop in levels. While uncommon, this is very concerning as we want to take the most prudent and cautious approach available to prevent an unplanned pregnancy. Moreover, data from systemic reviews shows that a very small number of patients can have decreases up to 47% of ethinyl estradiol concentrations. Putting all this together, the available data seems indicate that decreases are uncommon and likely due to random variation.


So this puts us in a precarious position: We can most likely expect birth control levels not to be negatively affected by fluconazole dosing but there have documented cases in which there are problems. With this information in hand, it is prudent to recommend back up birth control while taking fluconazole to mitigate the very low chance that birth control hormone levels are decreased as a cautious approach.


You mention in your question that you did use backup birth control but it failed. It would be a personal decision as to whether or not you want to use Plan B. The data shows that the vast majority of people have an increase in birth control levels while on fluconazole so there is a good chance you aren't at risk for pregnancy. However, since we do know that a small number of people are affected negatively by fluconazole dosing, if you want to use Plan B as an extra safety measure, that is certainly understandable and a prudent approach for many.

About the Pharmacist

Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of PharmacistAnswers.com. He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Brian.Staiger@PharmacistAnswers.com Office: 716-389-3076

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