Can antibiotics make birth control less effective?

Certain antibiotics that elevate enzymes can reduce the effectiveness of hormonal contraceptives like the pill.

The increase in enzymes from these medications can break down hormones more quickly and make hormonal birth control less effective. These antibiotics may also affect the rate of ovulation.

To avoid any chance of unintended pregnancy, your doctor may recommend using a secondary birth control method while you are taking certain antibiotics.

Nonhormonal forms of birth control, such as condoms or sponges, do not have any decrease in effectiveness from antibiotics.

How do hormonal contraceptives react with antibiotics? 

Enzyme-inducing antibiotics may affect hormonal contraception by changing how these forms of birth control work in the body.

How hormonal contraception works

Hormonal contraception works by changing the body’s typical reproductive system for a short period of time. This may include:

• stopping ovulation
• preventing fertilized eggs from implanting in the uterus
• increasing mucus in the cervix to make it harder for sperm to reach an egg

When antibiotics interfere with hormonal contraception, these factors that prevent pregnancy may not occur or occur less often, which means pregnancy is more likely.

Potential effects of enzyme-inducing antibiotics

Enzyme-inducing antibiotics, such as rifampin (rifampicin, Rifadin, Rimactane), work by increasing enzyme levels in the body. These additional enzymes can make the body process contraceptive hormones more quickly, reducing the amount left in your system.

A 2017 systematic review notes that rifampin can increase the frequency of ovulation and decrease exposure to estrogen or progestin. It also suggests that another antibiotic in the same class, rifabutin, had a similar effect.

A 2020 study reviewed adverse drug reactions in more than 107,000 people in the United Kingdom who were taking antibacterial or enzyme-inducing medications. Researchers stated that unintended pregnancy was 7 times more likely among those taking antibiotics and 13 times more common among those taking enzyme inducers.

If your doctor prescribes an antibiotic, ask about the specific type and how it may interact with your current medications, including hormonal birth control.

Which antibiotics can affect hormonal birth control?

Enzyme-inducing antibiotics that affect hormonal birth control include medications in the rifamycin group such as:

• rifampin (rifampicin, Rifadin, Rimactane)
• rifabutin (Mycobutin)

Antibiotics that do not affect hormonal birth control

Antibiotics with no proven effect on birth control include:

• amoxicillin (Amoxil)
• cephalexin (Keflex)
• ciprofloxacin (Cipro)
• erythromycin (Erythrocin)

A 2021 study looked at whether nonenzyme-inducing antibiotics can make hormonal birth control less effective but ultimately found insufficient evidence to support that conclusion.

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Combination of antibiotics and birth control

Although amoxicillin does not affect birth control, the combination product Talicia contains amoxicillin, omeprazole, and rifabutin. Rifabutin can affect the effectiveness of hormonal birth control. 

What birth control methods are affected by antibiotics?

Only hormonal birth control methods have a potential interaction with certain antibiotics.

Methods of hormonal birth control include:

• combined oral contraception pills
• progestogen-only pills
• contraceptive patch, such as Xulane
• vaginal ring, such as NuvaRing
• contraceptive implant, such as Nexplanon
• hormonal IUD, such as Mirena

Types of birth control not affected by antibiotics

Nonhormonal contraception methods do not interact with antibiotics or other medications. These types of birth control include:

• condoms
• copper IUD
• birth control sponge
• spermicide
• cervical cap

How do antibiotic side effects affect hormonal birth control?

Although most antibiotics do not stop hormonal birth control from working, the side effects of antibiotics may prevent your body from absorbing the contraception. 

Rifampin can result in irregular menstrual periods. You may also have breakthrough bleeding if you take this antibiotic with birth control. 

Common antibiotic side effects

Common side effects of antibiotic drugs include:

• nausea
• bloating
• headaches
• vomiting
• abdominal pain
• diarrhea

If you vomit within 3 hours of taking a combined pill or 2 hours of taking a progestogen-only pill, the medication may not have had enough time to get into your system to prevent pregnancy.

Diarrhea may also affect your body’s ability to absorb hormonal contraception. But the 2020 study of antibiotic effects on hormonal birth control did not find any link between diarrhea symptoms and unintended pregnancy.

Talk with your doctor or pharmacist about possible side effects before you begin any new medication. If you are taking hormonal birth control, they can discuss possible interactions and ways to manage your risk.

Summary

Most antibiotics do not affect hormonal birth control. Still, enzyme-inducing antibiotics, such as rifampin, can change the way hormonal birth control works and increase your chance of unintended pregnancy.

If you are taking rifampin, you may want to consider using a backup nonhormonal birth control method, such as condoms, until the antibiotic course is complete. Talk with your doctor about your individual risk and ways to manage it.

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