Does The Z-Pack Interact With Birth Control?

In our latest question and answer, the pharmacist discusses whether or not the Z-Pack (azithromycin) interacts with or lowers the efficacy of birth control pills.


Today I started taking the antibiotic azithromycin and I am also on birth control pills. I will be starting the placebo pills in 2 days. Am I protected during the placebo week? What about the following week when I begin my new pack of active pills?

Asked by Mary On Mar 22, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Mar 26, 2018

Z-Pack (Azithromycin) Birth Control PillsTaking a course of antibiotics while also using birth control can be a very concerning situation for many women. It is important to be protected against the serious consequence of unplanned pregnancy as well as prevent unwanted side effects that may result from antibiotics altering hormone levels.

Below, we discuss whether or not the Z-Pack (azithromycin) interacts with or affects birth control.

Does The Z-Pack Interact With Birth Control?

The jury is still out on just how much most antibiotics affect birth control, if at all. Current evidence points to the following:

  • Most antibiotics do not having a significant affect on birth control.
  • However, some studies do show that certain antibiotics, such as rifampin, definitively reduce hormone levels after taking birth control pills.

What Do The Studies Say?

There are many theories as to how antibiotics could potentially affect birth control, including:

  • Antibiotics, such as the Z-Pack, are known to cause changes to our normal bacterial gut flora. This could theoretically affect how estrogen and progestin from birth control pills are metabolized since our gut bacteria are involved in how our bodies process these hormones. This change in gut flora could potentially decrease the concentrations of the hormones in oral contraceptives, ultimately leading to spotting and a loss of contraceptive efficacy.
  • Some antibiotics, such as rifamycin, can alter hepatic metabolism, which can increase the speed at which birth control pills are metabolized.

However, most studies conclude that the majority of antibiotics do not significantly reduce the concentrations of oral contraceptives in the body and the efficacy of birth control pills is unchanged. The only antibiotics that have a definitive and well documented negative effect on oral contraceptive levels are ones from the rifamycin family of antibiotics such as rifampin. The Z-Pack (azithromycin) is not a rifamycin antibiotic.

On the other hard, and this is important to note, there are studies that note that there are a small number of individual patients who do in fact experience a significant decrease in concentrations of oral contraceptives when taking antibiotics and appear to ovulate as well (which birth control pills are supposed to suppress). This appears to be rare but the problem is that it can be difficult to identify exactly who is susceptible.

Overall, the general consensus appears to be:

  • Most antibiotics (including the Z-Pack) do not pose a problem to those on birth control.
  • Unfortunately, there are a small number of women who may be affected by antibiotics and they not easily identified. In addition, the true number of incidences of pregnancy while on antibiotics may be under-reported in total and the risk may be greater than we currently think.

Since unplanned pregnancy has major consequences, it may be prudent to use an additional method of contraception during short-term antibiotic use, just to be safe. One large study on the matter recommends the following:

"There is no way to determine which women are at risk, and, thus, some believe all women should be counselled regarding this interaction and the precautions they can take to avoid any unwanted pregnancy. The patient should decide on the alternative method of contraception because she must be comfortable with the method chosen.

Z-Pack And Antibiotics: Should You Use Backup Birth Control?

ZPack Backup Birth Control

In terms of how long to use a backup method, it is most often recommended to:

  • Use the backup method for 7 consecutive days of ACTIVE pills.

This is the usual recommendation in patients that could potentially experience changes in how their bodies absorb and metabolize their birth control pills. It is important to speak with your doctor as well to discuss your particular medical situation.

About the Pharmacist

Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of 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! Office: 716-389-3076

Recent Questions