You’ve probably heard at some point that antibiotics and birth control don't mix. Maybe you even saw a warning on your prescription that it could decrease the effectiveness of hormonal birth control methods like the pill. And obviously the last thing you want to worry about when treating a UTI or sinus infection is birth control failure. But here’s the thing: There’s no science to support this.
One study published in the journal Contraception, looked at oral contraceptive failures and found no association between antibiotic use and unplanned pregnancy, though the researchers noted that this study alone could not prove that there is not an elevated risk of birth control failure when taking antibiotics. A review of medical literature published in the Journal of the American Academy of Dermatology also found no connection between the vast majority of antibiotics, birth control, and unintended pregnancy, calling a possible link a “myth.” Older research has found no link between the antibiotics ciprofloxacin and fluconazole and decreased birth control effectiveness.
Despite that, this idea that all antibiotics will decrease the effectiveness of birth control lives on.
Research has found that the antibiotic rifampin, which is used to treat tuberculosis, and griseofulvin, a drug used to treat fungal infections, may decrease the effectiveness of hormonal birth control pills. These medications increase the activity of an enzyme in the liver that breaks down hormones, so the active hormones supplied by the pill get broken down faster than the body can use them to prevent ovulation, Jonathan Schaffir, M.D., an ob/gyn at the Ohio State University Wexner Medical Center, tells SELF. However, it’s super unlikely this information applies to you. “It is very rare that a woman of reproductive age in this country would receive either [medication],” he says.
A 1999 review in the Canadian Journal of Infectious Diseases looked at published papers between 1975 and 1998 that documented the interactions between antibiotics and oral contraceptives. They found that rifampin was the only antibiotic at that time that had been reported to reduce plasma estrogen concentrations. In their search, a few other antibiotics were associated with contraceptive failure in three or more case reports, including: ampicillin, amoxicillin, griseofulvin, metronidazole, and tetracycline. However, they concluded that these reports came from retrospective case studies, so a definitive interaction could not be proven.
Common, regularly-used antibiotics have “shown no clinical interference,” Brian Miller, M.D., assistant professor of Obstetrics & Gynecology at University of Cincinnati Health, tells SELF. “It’s just hearsay that doesn’t have any scientific reasoning.”
All birth control options have failure rates, which are determined by the percentage of people who will experience an unintended pregnancy within the first year of using a birth control method. According to a 2011 study in the journal Contraception, the birth control pill has a less than 1 percent failure rate with perfect use (when used consistently and correctly every single time) and a 9 percent failure rate with typical use (when you also factor in people who don't use it perfectly every single time).
The concern about antibiotics and birth control effectiveness is “mostly anecdotal and likely overstated,” Dr. Schaffir says. Knowing that birth control failures already happen as a result of human error, and that antibiotic use is so common, it's possible that these two issues often sync up by chance, he says. That might explain why your sister's friend's cousin swears she got pregnant after antibiotics messed up her birth control. As with any retrospective case study, it's not possible to pin that on the antibiotic.
As for the drug interaction warnings that can pop up, doctors are stumped, too. “We’re not 100 percent sure why pharmaceutical companies do this,” Fahimeh Sasan, D.O., assistant professor of obstetrics, gynecology, and reproductive medicine at the Icahn School of Medicine at Mount Sinai, tells SELF.
Andrea Fischer, a spokesperson for the Food and Drug Administration, which regulates medications in the U.S., tells SELF that the organization believes it’s “appropriate” to include a drug interaction warning for antibiotics and birth control pills. “The agency recognizes that, with the exception of rifampin-like drugs, the scientific evidence is limited regarding whether commonly prescribed antibiotics either reduce blood levels or the effectiveness of oral contraceptives,” she says. “Both antibiotics and oral contraceptives are prescribed frequently to women of childbearing potential; although one might expect to see a much higher rate of oral contraceptive failure if there is a drug-drug interaction, pharmacokinetic and clinical studies may not be of sufficient size to detect the interaction if a drug-drug interaction exists but is a relatively rare event.”
Fischer acknowledges that it’s also possible that some reports of unintended pregnancies in women taking antibiotics may simply be due to the already known failure rate of birth control pills. “However, taking all of the available information into account, at this time the agency’s conclusion is that this information should remain in the labeling for oral contraceptives,” she says.
For starters, always talk to your doctor about the medications you're taking and your risk of pregnancy if that's something you're worried about. You should also be aware of any side effects that could also be associated with decreased birth control effectiveness. For instance, diarrhea and vomiting (if severe) may impede the absorption of your pill, rendering it less effective. And if you're sick in bed with a fever for days, there's a chance you could miss a few pills, which would also decrease the effectiveness.
And if a few case studies showing a possible link are enough to make you wary of your birth control's ability to stand up to antibiotics, then you might want to use a condom or abstain from sex. If you really, truly do not want to get pregnant, you may appreciate that added security or warning label. And there's nothing wrong with that.
Related:
- 7 Things That Can Make Birth Control Pills Fail
- Birth Control Is Less Likely to Fail Now Than Ever Before
- What You Need to Know About Antidepressant Use During Pregnancy
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