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Will Antibiotics Affect Your Birth Control?

Will Antibiotics Affect Your Birth Control?

Get pharmacist-approved advice here.

  • Catherine Poslusny
    By: Catherine Poslusny
    Reviewed By: Janell Sanford, Pharm. D.
    Updated:

People use antibiotics to fight against bacteria that cause infection in their bodies.

Women use birth control pills to add friendly hormones to their body. So if you have sex, any swimming sperm will keep far away from your precious eggs (yay for birth control!).

Can you take both antibiotics and birth control at the same time?

You get an infection, and the doctor tells you to take antibiotics. But what if you're on birth control—will the pill still work?

Top researchers say that most women who take antibiotics—except for one called rifampinshould expect their birth control to work as expected. Planned Parenthood says the same thing more directly: antibiotics "won't change the effectiveness of your birth control."

But it's not always that simple. Researchers at Harvard Medical School haven't found enough evidence to say for sure that antibiotics don't affect birth control. Therefore, they have to say that taking antibiotics might affect birth control, just to be on the safe side. The paper insert inside your birth control pack might say that too.

The short answer is you probably won't get pregnant, but you can ask your doctor or health care provider to ensure that the antibiotics won't interfere with your birth control pills.

And if you're in a spot where you can't ask your provider for advice, or if you're just unsure, the best option would be to use a backup method like a condom when taking antibiotics.

Which antibiotics can interfere with birth control?

Rifampin is the only antibiotic that's been proven to make hormonal birth control unreliable. Also known as Rifadin and Rimactane, it's usually used to treat tuberculosis and other bacterial infections like meningitis.

To clarify, when we talk about hormonal birth control, we mean any type of birth control that uses hormones to keep you from getting pregnant. Note that you may hear birth control being called "contraception" or "contraceptives," which are the medical terms.

A list of different birth control methods that put hormones into your body are:

  • Birth control pills (also known as "the pill". Common brands include Apri, Mircette, Ortho-Cyclen, and Yaz.)
  • Birth control patches (Xulane)
  • Birth control shots (Depo-Provera)
  • Vaginal rings (Annovera and NuvaRing)
  • Intrauterine devices (Hormonal IUDs include Mirena, Kyleena, Liletta, and Skyla. This doesn't include copper IUDs, such as Paragard, that don't contain any hormones.)
  • Birth control implants (Nexplanon)

If you use the pill, the patch, or the ring, taking rifampin can make your birth control less effective, meaning there's a chance that it may not stop you from getting pregnant.

If you start taking rifampin, you should also use a backup birth control method to lower your chances of getting pregnant.

Fortunately, most other antibiotics shouldn't affect birth control at all. For example, this 2002 study, published in The Journal of the American Academy of Dermatology, found that these antibiotics aren't likely to interfere with hormonal birth control:

  • Ampicillin (Principen, Omnipen)

  • Ciprofloxacin (Ciloxan, Cipro, Neofloxin)

  • Clarithromycin (Biaxin)

  • Doxycycline(Vibramycin, Oracea, Adoxa, Monodox)

  • Metronidazole (Flagyl)

When it comes to amoxicillin, things aren't as clear cut, even though the consensus is that antibiotics do not interfere with birth control. Still, there have been a few reported cases of amoxicillin impacting the effectiveness of birth control pills. If your doctor prescribes you amoxicillin, they'll be able to give you a better idea of how (or if) it may affect your birth control.

The chances of getting pregnant while taking antibiotics and the pill

Using birth control is one of the most reliable ways to avoid getting pregnant. The CDC says that the pill, the patch, and the ring each prevent pregnancy in about 91 out of 100 women. In other words, the pill, patch, or ring should protect you 91% of the time from getting pregnant.

Keep in mind that this percentage goes up to 99% effective if you take the pill or use the patch or ring correctly every time (for example, if you take the pill every day, at the same time, as directed.)

But, unfortunately, some medications can make hormonal birth control more likely to fail. You may have heard that antibiotics fall into that category, but scientists say that the truth isn't that clear-cut like we mentioned above.

There have been rare reports of women who got pregnant while taking antibiotics and birth control. However, a few isolated reports aren't enough to assume that all antibiotics can lower birth control effectiveness.

Scientists seem to conclude that they haven't found a link between using antibiotics (except for rifampin) and a higher risk of pregnancy.

However, British researchers say that women taking birth control "should be warned that antibiotics may impair [birth control pill] effectiveness."

The scientific debate on whether antibiotics affect birth control

There's not much evidence that non-rifampin antibiotics can keep hormonal birth control from doing its job.

But the debate on this topic is still going strong. There are a couple of main reasons why people suspect that antibiotics may make hormonal birth control unreliable:

Did enough women participate in past studies? The researchers that studied the effects of antibiotics on birth control may have observed sample sizes too small to detect rare interactions between the two drugs.

Think of it this way: if a study only observes 25 people, there's a good chance that rare side effects (like those that only happen to 1 out of 1,000 women, or less) won't show up, even though they do happen to some people.

Even without possible interactions with antibiotics, there's always a very slight chance of getting pregnant while using hormonal birth control. Super rare drug interactions aren't likely to raise your risk of getting pregnant beyond the typical risk that comes with your chosen birth control method.

At the same time, however, an unexpected pregnancy is a life-changing event, and we understand that a slight risk isn't the same as no risk at all.

What about new evidence? A recent study published in August 2020 is causing some people to start rethinking their antibiotics and hormonal birth control stance.

The study, published in BMJ, the British Medical Journal, included information from thousands of drug interaction reports. The study's authors found that unintended pregnancies among women using hormonal birth control were 7 times higher in women who took antibiotics.

This number may be a little high, though, because people who believe that antibiotics caused their unintended pregnancy are more likely to report it. (This is called reporting bias, and it can impact a study's results.)

Because there's no full agreement on how antibiotics interact with hormonal birth control, you should always ask your doctor what they recommend for your specific situation. They may want to adjust your birth control dosage or recommend using an extra birth control method while you're taking antibiotics.

Can antibiotics cause irregular periods?

Antibiotics don't typically have any effect on your menstrual cycle. If you notice irregular periods around the time you're taking antibiotics, it's likely to be caused by illness or stress. They may not affect your period, but some antibiotics can make you more at risk for a yeast infection.

For more information, take a look at the pill package insert. It might say that women have had "contraceptive failure and breakthrough bleeding" after taking antibiotics like ampicillin.

Drugs like Rifampin interfere with birth control pills at the hormonal level. To understand why you need to know how birth control pills affect your hormones.

The science behind hormonal birth control

Hormonal birth controls contain some combination of the hormones estrogen and progestin. Depending on which kind of birth control you use, these hormones work in your body to do at least one of the following:

  • Prevent ovulation. Each cycle, the ovary releases a mature egg. This release is called ovulation. The days around your ovulation are the only time during each menstrual cycle that you can get pregnant. If you don't ovulate at all, you can't get pregnant.

  • Keep sperm from making it to the uterus. Birth control can do this by causing your cervical mucus---you've probably heard this referred to as "vaginal discharge"--- to get thicker. Thicker cervical mucus makes it incredibly hard for sperm to swim to an egg.

  • Make implantation unlikely. Hormonal birth control can make changes to your uterus lining that decrease the chances of a fertilized egg being implanted. Even if a sperm somehow makes it to an egg to fertilize it, you only get pregnant if it successfully implants in your uterine lining. No implantation, no pregnancy.

Rifampin can keep your birth control from doing its job by causing your liver to break down estrogen faster than it usually would. When estrogen gets broken down too quickly, it can't drive the changes in your body that normally keep you from getting pregnant.

Note: Copper IUDs don't use hormones to prevent pregnancy, so they won't be affected by any medicine that may change your hormone levels.

What other kinds of medication can interact with birth control?

Rifampin may be the only antibiotic proven to lower the effectiveness of hormonal birth control, but it's not the only drug that can do so. These medicines can also increase your chances of getting pregnant while taking hormonal birth control:

How long will birth control be affected by antibiotics?

The length of time that antibiotics or other drugs can affect birth control depends on which medicine you're taking. Some medications will only affect hormone levels while you're taking them. Others can have effects that linger for up to a week or even a month after you stop taking the medicine.

If you're prescribed something that makes your birth control less effective, your doctor will be able to tell you how long you should use a backup method of birth control.

What should you do to prevent pregnancy while taking medicine that affects birth control?

If you're worried that the medication you're taking may be affecting your birth control, you can always use a backup method to help prevent pregnancy, such as:

  • Male condoms: With typical use, prevents pregnancy in 87 out of 100 women.

  • Diaphragms and cervical caps: With typical use, prevents pregnancy in 83 out of 100 women.

  • Sponges: With typical use, prevents pregnancy in 63 to 86 out of 100 women, depending on whether or not they've already had a baby.

  • Spermicides: With typical use, prevents pregnancy in 79 out of 100 women.

Recap

Drug interactions are complicated, so it's always best to talk to your doctor about all prescriptions, over-the-counter drugs, and supplements you're taking before you start any new treatment.

If you start taking medicine that makes your hormonal birth control less effective, you may need to add a backup method, such as condoms, to prevent pregnancy.

Aside from rifampin, most antibiotics shouldn't affect whether your birth control works or not. However, more research is needed before we can be positive that different antibiotics never affect hormonal birth control. If you're anxious about a medication affecting your birth control, using backup protection may be worth it just for the peace of mind.

Sources

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