How Do Antibiotics and Other Medications Interfere With Birth Control?

Hormonal birth control is more than 90% effective at preventing unwanted pregnancies when used correctly. However, taking this kind of birth control and certain antibiotics together can reduce the effectiveness of the contraceptive. This is true of some other medications and supplements, as well.

Which antibiotics can affect birth control?

Antibiotics are used to treat infections caused by bacteria, such as urinary tract infections (UTIs), strep throat, and some sinus infections. 

In general, most antibiotics don’t affect how well  hormonal birth control works. But a couple of rifamycin antibiotics have been shown to interfere with the pill, patch, and vaginal ring methods.

Rifampin

Rifampin (Rifadin) is a rifamycin antibiotic. It’s commonly used to treat tuberculosis (TB). But it also often lowers estrogen and progestin hormone levels, making birth control less effective. 

Rifabutin

Rifabutin (Mycobutin) is another rifamycin antibiotic. It’s sometimes used to prevent Mycobacterium avium complex (MAC), an infection that tends to occur in people with HIV when their immune systems become very weak. More often, rifabutin is part of a combination medication used to treat stomach ulcers caused by Helicobacter pylori, or H. pylori. It may also be used off-label to treat TB. 

Rifabutin may lessen birth control’s effectiveness by slightly lowering estrogen and progestin levels. But this is less of a risk with rifabutin than it is with rifampin. 

Can amoxicillin or other penicillin antibiotics affect birth control?

No, penicillin antibiotics, like amoxicillin, don’t affect birth control.

It may seem like there’s a risk of interference because penicillin antibiotics can lower the number of bacteria in your gut. And these bacteria help your body absorb estrogen, so lower amounts of them could presumably interfere with how much estrogen from your birth control is absorbed. But studies have shown that penicillin antibiotics don’t affect gut bacteria enough to change hormone levels in your blood.

Which medications stop birth control from working?

In addition to rifamycin, these prescription medications and dietary supplements can potentially affect how well hormonal birth control works:

• Some anti-seizure medications

• Antiretrovirals (ARVs)

• St. John’s wort

• Exenatide, a diabetes-management medication

• Cholesterol-lowering medications

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Here is a rundown of the possible interactions between these medications and hormonal birth control, as well as some suggestions for safer alternatives. But this isn’t a complete list of medication interactions, so you should talk to your pharmacist or healthcare provider more detailed information.

Anti-seizure medications, or antiepileptics

Antiepileptics are often used to prevent seizures. They are also sometimes taken for migraines, nerve pain, and some mental health conditions. But some anti-seizure medications can make your birth control less effective by lowering hormone levels in your blood. 

These are some common anti-seizure medications that may interact with birth control:

• Carbamazepine (Tegretol, Carbatrol)

• Lamotrigine (Lamictal)

• Oxcarbazepine (Trileptal)

• Phenobarbital

• Phenytoin (Dilantin)

• Topiramate (Topamax)

In the cases of lamotrigine and topiramate there’s only a risk of interaction at certain dosages. For lamotrigine, that dosage is 300 mg per day or more and, for topiramate, it’s more than 200 mg per day. 

Also, taking hormonal birth control may make lamotrigine and valproic acid less effective at preventing seizures.

Antiretrovirals

These medications are used to prevent HIV from multiplying, in order to keep the infection under control. But some ARVs can interact with birth control. In some cases, an ARV may make birth control less effective, while, in others, birth control may make ARV levels higher, causing side effects.

The good news is that there are some safe contraception-ARV combinations. Your healthcare provider can give you a recommendation based on your specific needs.

St. John’s wort

St. John’s Wort (Hypericum perforatum) is an over-the-counter herbal supplement sometimes used to treat symptoms of depression. But this natural remedy can also mess with your birth control by encouraging certain liver proteins to quickly break down the contraceptive and clear it from your body. 

Exenatide

Exenatide (Byetta, Bydureon BCise) is an injectable medication used to help control blood sugar levels in people with Type 2 diabetes. It slows down the emptying of the stomach, which can affect how the hormones in oral birth control pills are absorbed by the body. 

Luckily, in the case of Byetta, this interaction can be managed by taking the medications at different times. To avoid this issue, you’ll want to take your birth control pill at least an hour before administering Byetta. 

If you’re taking the once-weekly version of exenatide (Bydureon BCise), talk to your healthcare provider about birth control options that are less likely to interact with the medication.

Cholesterol-lowering medications

Some medications for high cholesterol may also affect how your body absorbs estrogen. Colesevelam (Welchol), colestipol (Colestid), and cholestyramine (Prevalite) may bind to your birth control in your gut and prevent it from being absorbed.

Like with Byetta, you can still take both medications as long as you space them out. If you’re taking colesevelam, you’ll need to take your birth control pill 4 hours before the cholesterol-lowering medication. 

Does melatonin affect birth control?

It’s unlikely that melatonin will have an effect on how well your birth control works. There have even been some studies that show melatonin may help increase fertility (not in relation to birth control).

That being said, more research is needed. If you’re concerned about a possible interaction between melatonin and your birth control, reach out to your healthcare provider. They can advise you on alternative sleep aids.

Will Plan B work if I am taking antibiotics or other medications?

Emergency contraception, like Plan B, may not work if you are currently taking or have recently taken:

• The anti-seizure medications discussed above

• Rifamycin antibiotic

• Antiretrovirals

• St. John’s wort

In some of these cases, the best method of emergency contraception is usually the copper IUD (ParaGard). This will need to be inserted by a trained healthcare professional within 5 days of having unprotected sex. For more information about emergency contraception, see our full article here.

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Written by:

Ross Phan, PharmD, BCACP, BCGP, BCPS

Ross Phan is a board-certified clinical pharmacist. She has roughly two decades of healthcare experience — with most of her experience being pharmacy related.

Reviewed by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

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