According to an analysis published in the peer-edited medical journal BMJ Evidence-Based Medicine, unintended pregnancies were seven times more commonly reported with antibiotic use versus the use of control medicines. While an antibiotic called rifampin—which Mary Jane Minkin, MD, a board-certified OB/GYN and founder of Madame Ovary, says is "very rarely used"—has long been acknowledged by health-care professionals as interfering with birth control, it is not one of the antibiotics included in the analysis. Instead, the research looked at the effects of more common antibiotic medications, like amoxicillin (which is often used to treat urinary tract infections).
While this may seem like an alarming development, Dr. Minkin assures me otherwise. "This isn't a lot of 'hot news'," she says. "We have always told women that use of an antibiotic may render contraceptives less effective."
"To be on the safe side, it is quite reasonable to tell [people] to use back-up condoms for the rest of the cycle in which they are using the antibiotics." —Mary Jane Minkin, MD, OB/GYN
She explains that antibiotics rev up the enzyme systems in the body that metabolizes birth control pills, which can result in a diminished amount of contraceptive left to protect you from pregnancy. Since birth control pills these days are often low in dosage to begin with—they used to contain 50 or 80 micrograms of estrogen, and now they contain 20, 30, or even just 10—this can be problematic. "So to be on the safe side, it is quite reasonable to tell [people] to use back-up condoms for the rest of the cycle in which they are using the antibiotics," Dr. Minkin says.
However, doctors don't always provide such blanket advisories. According to Leena Nathan, MD, an assistant clinical professor and OB/GYN at UCLA Health, doctors are advised to issue warnings around Rifampin, some anti-seizure medications, antiretrovirals (used to treat HIV), and an anti-fungal medication called Griseofulvin. Beyond that, she says there are no interactions advised with respect to birth control, and she notes that she probably wouldn't personally change her recommendations based on this new analysis without further evidence.
To be clear, even the study's authors say that more research needs to be done to confirm the risk of pregnancy with the use of the antibiotics they studied. But regardless of which school of thought your doc belongs to, it certainly can't hurt to take extra precautions (like condom use) if you're prescribed an antibiotic while on the Pill—especially since, as Dr. Minkin points out, most antibiotics are taken for just a short period of time. If you're needing to be on antibiotics for a longer period of time, Dr. Minkin recommends consulting with your gynecologist about adjusting your hormonal contraceptive or switching to another form of birth control (like an IUD) that would not be affected by antibiotic usage.
More research should certainly be done to give us some concrete answers. In the meantime, be sure to consult your doctor when prescribed antibiotics (or anything!) and maybe, you know, wrap it up—just in case.
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