Can Antibiotics Affect Menstruation?

woman looking sick
Only one antibiotic has been proven to affect the menstrual cycle: rifampin.

If you're a woman who's ever been prescribed antibiotics while taking oral contraceptives, you're probably familiar with the warning label that advises a second form of birth control while taking the medication. And if antibiotics can interfere with oral contraceptives, it's understandable that you might assume that antibiotics can also affect your menstrual cycle. Do a quick sweep of the Internet, and you'll find a slew of panicked women wondering if antibiotics have caused their missed periods (or unintended pregnancies). But you'll also notice a lack of fact-supported, medical answers that confirm their suspicions. Most antibiotics come with a hefty list of possible side effects, but menstrual irregularities are never on there.

If there's no scientific link between most antibiotics and the menstrual cycle, why are so many women convinced that antibiotics make their periods go out of whack?


Stress could be the culprit. Whether you're frazzled because of work, a traumatic event or just an extra-demanding month, stress is a well-known cause of late periods. And an infection is an intense form of stress for your body to endure. So, if you're taking antibiotics for an infection -- especially one in the reproductive system -- it's entirely possible that your stressed-out body will decide to take a little break from your regularly scheduled monthly visitor. And it's also possible that you will then assume that antibiotics are the guilty party.

There's only one antibiotic that has been proven to affect the menstrual cycle: rifampin, a powerful drug that's used to stop the spread of tuberculosis-causing bacteria in the body. Rifampin is known to cause quite a few menstrual side effects in some women, including painful and irregular periods, abnormal bleeding and the absence of periods (amenorrhea). Rifampin can also decrease the effectiveness of oral contraceptives. For reasons that aren't completely clear, it causes the liver to quickly flush out two of the hormones in birth control pills that suppress ovulation. So, if you're taking rifampin and the pill simultaneously, there's a chance you could ovulate. But there's no evidence that this happens with any other type of antibiotic.

To be sure, there's kind of a black hole on this subject in terms of academic studies -- some of the more well-known ones date back to the 1940s and '60s. In cases like this with a lack of hard facts (and with such high stakes as unintended pregnancies), there's a tendency to err on the side of caution. Hence the warning labels and widespread confusion. But the next time you're taking antibiotics and your period doesn't behave normally, don't be so quick to blame the medication. Remember that your body is under stress, and it's better to keep taking the antibiotics to get your system back on track.


Antibiotics Menstruation FAQ

Can antibiotics cause a late period?
There's no scientific link between most antibiotics and the menstrual cycle, yet many women are convinced that antibiotics make their periods go out of whack. Often, the stress of being sick is enough to cause a delay in your period, as it's a well-known culprit when it comes to late and missed periods.
Can antibiotics affect your period flow?
Taking antibiotics doesn't generally have an impact on your period. Only one antibiotic, rifampin (used as a treatment for tuberculosis), has been shown to have any effect on your period, including painful and irregular periods, abnormal bleeding and the absence of periods.
Can you get pregnant on antibiotics?
While antibiotics can't make you pregnant or cause a pregnancy test to falsely come back positive, some may make birth control pills less effective, which could result in pregnancy. In fact, many antibiotic information sheets come with a warning. However, little research has been done in this, so there's not much evidence that antibiotics actually interfere with birth control pills. Some doctors suggest using a second type of birth control while taking antibiotics, just to be safe.
Can I treat an infection while menstruating?
Yes, taking antibiotics has no known effects on menstruation. Talk to your doctor as soon as you think you have an infection, regardless of where you are in your cycle.
Do antibiotics affect fertility?
Studies have shown that several antibiotics like tetracycline, penicillin, erythromycin can adversely affect male sperm and fertility. These effects should stop within three months of stopping the course of antibiotics. However, little research has been done on the effects of frequent antibiotic use on women's fertility.

Lots More Information

Related Articles

  • Barditch-Crovo P., C.B. Trapnell, E. Ette, H.A. Zacur, J. Coresh, L.E. Rocco, C.W. Hendrix, C. Flexner. "The effects of rifampin and rifabutin on the pharmacokinetics and pharmacodynamics of a combination oral contraceptive." Clinical Pharmacology and Therapeutics, April 1999. (Oct. 7, 2014)
  • Benaroch, Roy. "Oral Contraception and Antibiotics." WebMD, May 26, 2011. (Oct. 7, 2014)
  • Freedman, Megan. "Birth Control Pills and Antibiotic Use." Local Health, Dec 15, 2013. (Oct. 7, 2014)
  • MedlinePlus. "Rifampin." (Oct. 7, 2014)
  • Winderlich, Melanie. "Stress and Your Menstrual Period: A Cycle That You Can Break." Everyday Health, Feb. 17, 2010. (Oct. 7, 2014)