5 Plan B Interactions to Consider
Key takeaways:
Plan B One-Step (levonorgestrel) is an emergency contraceptive pill taken after unprotected sex to prevent pregnancy. A number of other medications can make it less effective.
Plan B may interact with topiramate (Topamax), carbamazepine (Tegretol, Equetro), and St. John’s wort. Efavirenz (Sustiva) and rifampin (Rifadin) can also interact with Plan B.
Paragard (the copper IUD) can be an emergency contraception alternative if you take medications that interact with Plan B.
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Table of contents
Plan B One-Step (levonorgestrel) is an over-the-counter (OTC) emergency contraception pill that can prevent pregnancy after unprotected sex. It’s a hormonal birth control that can also be taken if your regular birth control method fails (like a condom breaking).
Typically, Plan B is up to 89% effective if taken within 3 days (72 hours) of unprotected sex. But there are several Plan B interactions that can lower its effectiveness. It’s important to talk to your healthcare provider or pharmacist about interactions before taking this emergency contraceptive. That way, you can discuss steps to take to avoid Plan B interactions if needed.
Below, we highlight five Plan B interactions to be aware of. Keep in mind that this is not a complete list of all possible interactions.
Good to know: Plan B is available under several different brand and generic names, including levonorgestrel 1.5 mg, EContra One-Step, and AfterPill. Like Plan B, these are all hormonal contraceptives that contain levonorgestrel (a type of estrogen).
1. Topiramate
Topiramate (Topamax) is a medication that can help prevent migraines and certain types of seizures. Because of how your body breaks down (metabolizes) topiramate, it can speed up how fast your body gets rid of Plan B. This Plan B interaction can make it less effective and increase your chances of pregnancy.
Some experts believe that 200 mg per day or less of topiramate don’t affect Plan B. But the manufacturer of Plan B still warns of the possible interaction. So it’s better to err on the side of caution and assume Plan B may be less effective if taken with any amount of topiramate.
2. Other seizure medications, such as carbamazepine
Carbamazepine (Tegretol, Equetro), along with some other seizure medications, can also interact with Plan B. Seizure medications may lower the level of Plan B in your body, potentially making it less effective. Other seizure medications that interact with Plan B include phenytoin (Dilantin) and phenobarbital.
It’s important to note that there’s a lack of studies focusing on this Plan B interaction. So we don’t know exactly how likely this interaction is. But similar to with topiramate, it’s best to presume Plan B may be less effective if you also take seizure medications.
3. St. John’s wort
St. John’s wort is an OTC herbal supplement that some people take to help with symptoms of depression. St. John’s wort can cause Plan B to clear from the body faster. This may make it less effective at preventing pregnancy.
4. Efavirenz
Efavirenz (Sustiva) is a medication prescribed along with other medications to treat HIV. Because of how efavirenz works, it can decrease the amount of Plan B in your body. This means it may be less effective.
5. Rifampin
Rifampin (Rifadin) is a medication prescribed to treat tuberculosis. Rifampin is notorious for interacting with many medications, including Plan B. Rifampin can speed up how fast your body breaks down Plan B. This can lower its effectiveness.
What can you do to manage these Plan B interactions?
It’s ideal to talk to your healthcare provider or pharmacist about Plan B interactions before taking it. Having a medication list handy is very useful and can help guide your healthcare team in making the best choices for you.
It’s important not to change or stop taking any medications without talking to your provider. It’s unlikely that they’d ask you to stop your other medications to avoid Plan B interactions. Instead, they may recommend a non-hormonal emergency contraceptive, such as Paragard, the copper intrauterine device (IUD).
Another potential alternative would be to take an extra dose of Plan B. This can boost the level of Plan B in your body and may help overcome interactions. But it’s important to talk to your provider before doing this. This method hasn’t been studied enough, so experts don’t know how effective a double dose is when it comes to managing Plan B interactions. An extra dose can also make side effects, such as nausea and vomiting, more likely to happen.
The bottom line
Plan B One-Step (levonorgestrel) can interact with several medications. These include topiramate, carbamazepine, and other seizure medications. St. John’s wort, efavirenz, and rifampin are also problematic. These medications can all make Plan B less effective.
Remember to talk to your healthcare provider before making any changes to your medications. They may suggest an alternative to Plan B, like Paragard (the copper IUD), to help you manage these interactions.
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References
American Health Packaging. (2023). Rifampin [package insert].
Glenmark Therapeutics Inc., USA. (2023). Levonorgestrel [package insert].
Haeger, K. O., et al. (2018). State of emergency contraception in the U.S., 2018. Contraception and Reproductive Medicine.
Reimers, A., et al. (2015). Interactions between hormonal contraception and antiepileptic drugs: Clinical and mechanistic considerations. Seizure.
Sarayani, A., et al. (2023). Real-world effect of a potential drug-drug interaction between topiramate and oral contraceptives on unintended pregnancy outcomes. Contraception.
University of Liverpool. (n.d.). Potential interaction: Efavirenz (EFV): Levonorgestrel (emergency contraception). HIV Drug Interactions.
Westminster Pharmaceuticals, LLC. (2023). Phenobarbital tablet [package insert]. DailyMed.
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