Do antibiotics reduce birth control effectiveness?

• The vast majority of antibiotics do not interfere with hormonal birth control, with the notable exceptions of rifampin and rifabutin, which can significantly lower contraceptive effectiveness.
• Rifampin and rifabutin work by accelerating the liver's breakdown of hormonal contraceptive ingredients, causing hormone levels in the bloodstream to drop and raising the risk of unintended pregnancy.
• Common antibiotics such as amoxicillin, azithromycin, doxycycline, and ciprofloxacin have shown no evidence of diminishing hormonal contraceptive protection in clinical research.
• Women taking rifampin or rifabutin should use a backup contraceptive method—such as condoms—during the full course of treatment and for seven days after finishing short-term therapy, or two weeks after completing longer courses.

If you rely on birth control to prevent pregnancy, you likely use one of several available options—ranging from barrier methods to pills, patches, rings, or implants. Birth control encompasses any medication, device, procedure, or surgical method designed to prevent pregnancy from occurring. If you take a hormonal contraceptive such as a pill, patch, or vaginal ring, certain medications can interfere with how well it works. While the majority of antibiotics pose no risk to your birth control's reliability, a small number do. Understanding which ones matter—and how they affect your protection—is essential information for anyone using hormonal contraception.

Taking antibiotics and birth control together

According to Kim Langdon, MD, OB-GYN and founder of Coologics, "Most antibiotics don't affect birth control." The two antibiotics that do pose a problem are Rifadin (rifampin) and Mycobutin (rifabutin), though they are prescribed far less frequently than other antibiotic options, and research on the magnitude of their impact remains incomplete.

Erika Gray, Pharm.D., chief medical officer and co-founder of Toolbox Genomics, notes that rifampin and rifabutin may interfere with several hormonal birth control methods:

• Combined oral contraceptives (pills containing both synthetic estrogen and progestin)
• Progestin-only pills (the minipill)
• Plan B (levonorgestrel emergency contraceptive, effective within 72 hours of intercourse)
• Contraceptive patches (skin-applied estrogen and progestin release)
• Vaginal rings (flexible rings releasing estrogen and progestin)
• Ella (ulipristal emergency contraceptive, effective within 120 hours of intercourse)

These medications do not reduce the effectiveness of IUDs, the Depo Provera injection, hormonal implants, or barrier methods such as condoms, diaphragms, or contraceptive foam.

With perfect adherence—taking the pill at the same time daily without missing doses—oral contraceptives achieve up to 99% effectiveness. In typical real-world use, where some doses are occasionally missed, the rate drops to approximately 91%. Since most antibiotics do not influence contraceptive efficacy, pregnancy risk mirrors typical-use rates unless rifampin or rifabutin is involved, according to Dr. Gray.

According to Planned Parenthood, diarrhea or vomiting lasting more than 48 hours, or the use of laxatives, can also compromise oral contraceptive effectiveness. In such cases, a backup contraceptive method should be used for seven days.

What the research says

A 2018 study demonstrated that rifampin at 600 mg daily and rifabutin at 300 mg daily both reduced birth control pill effectiveness by lowering blood levels of ethinyl estradiol (a synthetic estrogen) and norethindrone (a synthetic progestin).

Dr. Langdon emphasizes that becoming pregnant while on hormonal birth control and taking non-rifamycin antibiotics is unlikely. A 2017 systematic review found no evidence of interactions between hormonal contraceptives and non-rifamycin antibiotics, supporting this conclusion.

Rifampin

Rifadin (rifampin) is prescribed to treat tuberculosis and meningitis. This antibiotic has a documented interaction with hormonal birth control that can reduce its protective effect. According to Dr. Gray, "Rifampin affects the way the body metabolizes hormones, specifically estrogen and progestin, which are the key components of most hormonal birth control methods."

The mechanism involves liver enzymes: rifampin activates the enzymes responsible for breaking down and eliminating hormones from circulation. This accelerated metabolism causes contraceptive hormones to be processed and removed from the body faster than normal, rendering them less effective and substantially increasing the likelihood of unintended pregnancy.

Rifabutin

Mycobutin (rifabutin) treats tuberculosis, Mycobacterium avium complex disease (MAC), and H. pylori infection. Similar to rifampin, rifabutin can diminish hormonal birth control's effectiveness by accelerating the breakdown of estrogen and progestin through increased liver enzyme activity, as Dr. Gray explains. This process causes blood hormone levels to decline, reducing contraceptive protection.

Other medications that may affect birth control

Beyond antibiotics, several medication classes may interact with hormonal contraceptives and reduce their reliability, according to Dr. Gray:

• Anticonvulsants: carbamazepine, oxcarbazepine, phenytoin, and topiramate
• Antifungals: griseofulvin, fluconazole, metronidazole, and itraconazole
• Antiretrovirals for HIV: ritonavir and efavirenz
• Herbal products: St. John's Wort, vitamin C, and melatonin (though additional research is needed)
• Actos (pioglitazone) for diabetes
• General anesthesia agents such as Sugammadex
• Emend (aprepitant), used for nausea prevention
• Tracleer (bosentan) for pulmonary hypertension
• NSAIDs including ibuprofen and naproxen

Do amoxicillin and other common antibiotics affect birth control?

Azithromycin, commonly known as a Z-Pak, is a broad-spectrum antibiotic used for various bacterial infections. According to Dr. Gray, "There is no strong evidence suggesting that azithromycin significantly affects the effectiveness of hormonal birth control." This finding applies to most antibiotic classes, including:

• Penicillins (amoxicillin, ampicillin)
• Cephalosporins (cephalexin, cefuroxime)
• Macrolides (azithromycin, erythromycin)
• Tetracyclines (doxycycline, tetracycline)
• Fluoroquinolones (ciprofloxacin, levofloxacin)

Effectiveness of Plan B and Ella while on antibiotics

The majority of antibiotics do not interfere with Plan B or Ella (emergency contraceptives), but rifampin is a documented exception—it reduces their effectiveness. Anyone taking rifampin or considering an emergency contraceptive should discuss potential drug interactions with a healthcare provider beforehand.

Birth control effectiveness after finishing antibiotics

Most antibiotics do not significantly compromise birth control reliability, with rifampin and rifabutin being the notable exceptions. If you are prescribed either of these medications for a short-term infection, your healthcare provider should recommend using a backup contraceptive method—such as condoms—throughout your treatment and for seven days after completing the course to prevent unplanned pregnancy. For longer-term therapy with rifampin or rifabutin, maintain backup contraception during the full treatment period and for two weeks following the final dose.