You may have heard that if you take antibiotics with your hormonal birth control (pills, patches, shots, implants, or vaginal rings) it can raise your chance of getting pregnant. With one exception, rifamycin antibiotics, this is a myth.
“I don’t hear this bit of folklore as much as I did when I started practicing medicine, but the misperception that this is a problem is still out there,” says Valerie French, MD, MAS, associate professor of obstetrics and gynecology at the University of Kansas Medical Center.
The truth is that the types of antibiotics most often used, whether they’re taken as pills or through an IV, don’t affect birth control at all, she says.
This includes these antibiotics used to treat common bacterial infections:
- Amoxicillin
- Azithromycin
- Clarithromycin
- Doxycycline
- Erythromycin
- Metronidazole
- Quinolones (ciprofloxacin, ofloxacin)
These are called “broad-spectrum antibiotics” because they can fight many different kinds of bacteria that cause infections.
If you’re taking them, or any antibiotic other than rifamycin types, you can be confident that your birth control will work as usual, French says. This goes for birth control pills used for emergency contraception as well.
What Does the Research Say?
A 2018 American Journal of Obstetrics & Gynecology review of 29 studies looked at this issue. It found no proof that any antibiotics other than the rifamycins affect how well your birth control works.
Other research and experts agree. This includes the CDC, the American College of Obstetricians and Gynecologists, and the World Health Organization.
They all say you can take non-rifamycin antibiotics without concerns about a higher risk of an unplanned pregnancy and without using a back-up birth control method. This includes antibiotics you use long-term, such as erythromycin to treat acne.
What Are Rifamycin Antibiotics?
Doctors use rifamycin antibiotics (rifampin, rifabutin, rifapentine) to treat bacterial infections, mainly tuberculosis. They’re not often used for that or any other condition, though.
Doctors sometimes call these drugs “enzyme-inducing antibiotics.” That’s because they raise levels of enzymes in your body, including those that can affect hormonal birth control. It’s this process that can raise your chance of an unplanned pregnancy.
Hormonal birth control works because it enters your bloodstream and changes your hormones so that your ovaries don't produce an egg. Your liver then breaks down, or metabolizes, the hormones in the birth control. When you take rifamycin antibiotics, your liver breaks down your hormonal birth control much faster.
That means your birth control doesn't work as well to turn your ovaries off, French says.
What Should I Do if I Take a Rifamycin Antibiotic?
Rifamycin antibiotics don’t affect progesterone-only injections (Depo-Provera) or intrauterine devices (IUDs) or systems (Liletta, Mirena, Kyleena, Skyla). If you use one of these, you don’t need to add a back-up birth control method.
If you use a pill, patch, implant, shot, or vaginal ring for birth control, you should use a back-up method, such as condoms or a diaphragm. To prevent pregnancy, you’ll need to use your back-up birth control for 28 days after you finish your rifamycin antibiotic.
If you need to take a rifamycin antibiotic for more than 2 months, ask your doctor if you should switch to a different kind of birth control. Rifamycin doesn’t affect copper IUDs or barrier birth control methods like condoms or cervical caps.
Do Antifungals Affect Birth Control?
You can use most common antifungals without worrying that they’ll stop your birth control from working. This include two drugs doctors often use to treat vaginal yeast infections:
Griseofulvin is an antifungal doctors use to treat infections of the skin and scalp. It can raise your odds of an unplanned pregnancy if you use it with combined birth control pills (pills that contain both estrogen and progesterone).
If you take combined pills, use a backup birth control method for a month after your last dose of griseofulvin.
What Else Should I Know About Birth Control and Antibiotics?
Some antibiotics (and illnesses you get them for) can cause nausea, vomiting, and diarrhea. Too much of this could mean your body can’t absorb enough of the hormones in your birth control pills to prevent pregnancy.
Your body probably won’t take in enough hormones if you vomit or have a lot of diarrhea within 2 hours after taking a progesterone-only pill (the minipill) or less than 3 hours after taking a combined birth control pill. If this happens, take another pill right away, and your next pill at your regular time.
If you don’t get sick again, you’re still protected against pregnancy. If your vomiting or diarrhea goes on for more than a day, your pill may not work as well to prevent pregnancy. Keep taking your pills, but use a back-up birth control method and check with your doctor or pharmacist about what to do next.
Finally, remember that no birth control method prevents 100% of pregnancies. You’ll get the most protection from your hormonal birth control if you:
- Take your pills at the same time each day.
- Keep patches in place and change them once a week.
- Get your shot on schedule every 3 months.
- Replace your vaginal ring as often as directed.
