Here’s a health rumor that just won’t quit: Taking antibiotics makes hormonal birth control less effective—or even ineffective. Perhaps you heard this from your primary care doctor or the doc you saw at an urgent care clinic, or because “a friend of a friend” got pregnant this way. Or maybe you actually took the time to read the inserts pharma companies supply with an antibiotic, which often list this as a potential interaction.
It’s not clear how this rumor got started, says Susan E. Pesci, an OB/GYN, family planning specialist, and clinical instructor at Montefiore Health System in New York City, but it is mostly a rumor. She says she fields calls from patients asking if it’s okay to take antibiotics with the combination birth control pill (i.e. a mix of estrogen and progestin). Pesci offers her reassurance that everything will be fine. “The reality is that there are very few antibiotics that interfere with oral contraceptives,” she says.
Mary Jane Minkin, clinical professor of obstetrics, gynecology, and reproductive sciences at the Yale University School of Medicine, agrees. “The impact of antibiotic therapy tends to be exaggerated,” she says. “In general, if a woman is taking a week’s worth of antibiotics for a sinus infection or bladder infection, she shouldn’t have to worry.”
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There is one antibiotic that certainly does pose a problem, but it’s very rarely prescribed. It’s called rifampin, and is commonly used for tuberculosis, an infectious disease that’s listed in the National Institutes of Health’s rare diseases information center. “We don’t see this much in the US,” Pesci says.
Here’s how rifampin affects birth control: “All drugs are processed either in the liver or kidneys. This antibiotic can cause the liver to hyper-process the birth control pill, so you have less of it in your system,” Pesci says. Basically, it eliminates the pill from your body faster, decreasing the amount of the medication in your bloodstream. The hormones in the pill prevent ovulation, or the release of an egg, and if you don’t have enough hormone to do that, an egg could be released and you could get pregnant if you have unprotected sex. Rifampin could also affect the patch and the ring.
And while this is not true for all antibiotics, the rumor persists. A quick Google might send you to the Walgreens website where they very correctly say that rifampin interacts with birth control pills, but then also list eight far more common antibiotics—including penicillin and amoxicillin—that interfere with the pill “to a lesser extent.” That’s enough to make you freak out.
Even some research treads carefully. One 2015 study found that about 30 percent of patients said they knew about the potential interaction, and the authors concluded that, despite conflicting evidence, people should at least be aware of the connection, since unintended pregnancy is, well, not to be taken lightly. A 2011 study that looked at the topic didn’t find a connection between the two, though the authors note that they could not rule out antibiotic-related birth control failure. Remember that the pill is only 91 percent effective with typical use (and 99 percent effective with perfect use), so it’s possible that some cases of women getting pregnant while taking antibiotics could be due to normal pill failure rates.
It’s also worth noting that if you’re on antibiotics and have vomiting or diarrhea, you may not be absorbing your pill properly. In this case, it’s not the antibiotic you’re taking that’s the problem, but the illness itself. “If there’s any question about if you’ve missed or haven’t absorbed pills over an extended period of time, use backup birth control just in case,” Pesci says. In this case, “extended period” means two days in a row—at that point, there is a possibility you could ovulate and get pregnant. The Mayo Clinic says if you vomit within two hours of taking a pill, you should use backup contraception for the next week. (These are also good things to know in the event that you ever get food poisoning or a stomach virus.)
While we’re on the subject of things that mess with birth control, there are a few non-antibiotic medications that can change the effectiveness of the pill, patch, or ring. These include some epilepsy and seizure drugs (including topiramate, which is also used to treat migraines), and certain antiretroviral medications for HIV treatment, the antifungal griseofulvin (which is used for ringworm and athlete’s foot), and St. John’s Wort (an herbal supplement some people take for depression).
Here’s what you should do to make sure your hormonal birth control is in working order:
Consider a higher dose
If you’re taking an antibiotic for long-term therapy (for tuberculosis or, say, chronic UTIs), Minkin advises checking with your provider to see if using a higher-dose birth control is an option. “Many women are taking pills that contain 20 micrograms of estrogen. We have plenty of pills available, which are quite safe, which contain 30, 35, or even 50 micrograms of estrogen, which will take care of the hyped-up metabolism of the birth control pill,” she says.
Think about an IUD
If you’re taking one of the medications listed above for a chronic condition, an IUD may be a good option for you. “If you need regular contraception, and do take some of these medications regularly, you may want to consider an IUD,” Minkin says. These devices work directly in the uterus, so there’s no concerns about sped-up metabolism in the liver.
Always talk to your doctor
No matter what you’re taking, be it a medication prescribed by another doctor or an herbal supplement, you want to double check with your doctor that there are no potential interactions.
Use a backup if it makes you feel better
And if you want to err on the more cautious side and use a backup birth control method (like condoms) while taking an antibiotic, then by all means, go for it. “I’m always happy to have folks [err] on the cautious side of things,” Minkin says. Just know that you don’t have to.
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