When you’re about to take a morning-afternoon pill, you trust that the drug will do what it needs to do to prevent pregnancy without any issues. WhileMAP and Plan B type ECs are entirely safe, reliable, and very easy to use,
certain medications and supplements you may be taking can reduce the EC’s effectiveness, cutting into its ability to delay ovulation.
Being aware of what drugs and supplements interfere with morning-after pill effectiveness can give you more control, and keep you from becoming pregnant.
Medications That May Reduce Morning After Pill Effectiveness
Let’s take a look at the different classes of medications that affect Morning After Pill’s effectiveness.
Anti-Seizure Medications (e.g., Topamax, Carbamazepine, Phenytoin)
Anti-seizure medications (also known as anticonvulsants) are some of the most well-known drugs that affect the morning-after pill’s effectiveness. They are very powerful enzyme inducers, meaning that they essentially push your liver into “high-speed” mode and break down the active ingredient in morning after pills (levonorgestrel)faster than normal.
Here are a few notable medications to point out:
- Topiramate (Topamax): Topamax speeds up hormone metabolism, meaning Plan B may not have enough time to work in your body. However, research suggests low doses (under 200 milligrams) of the anticonvulsant drug may not affect Plan B, but you’ll want to take that up with your healthcare provider to confirm when you next see her.
- Carbamazepine (Tegretol, Carbatrol, and Equetrol): This is another strong enzyme inducer. Carbamazepine and emergency contraception don’t mix too well. You are advised to seek an alternative EC agent.
- Phenytoin (Dilantin, Phenytek), phenobarbital (Luminal, Sezaby), and oxcarbazepine (Trileptal, Oxtellar XR): These anticonvulsants have the same story. Do not use MAP , Plan B or it’s generics for EC. Use another EC product.
If you’re taking any of these medications, MAP and Plan B or its generics are not your best option for emergency contraception. Ella or a copper IUD will be more effective.
Antibiotics and Antifungals
When it comes to antibiotics, there’s a lot of confusion. Many people think that antibiotics in general “mess” with birth control, but that’s mostly referring to daily hormonal birth control pills, not emergency contraception. Most antibiotics do not affect how your body processes levonorgestrel ECs.
The following list of commonly prescribed antibiotics will not weaken the action of levonorgestrel type ECs to do their work in delaying ovulation.:
- Amoxicillin (Amoxil, Moxilin, Sumox, and Trimox)
- Azithromycin (Zithromax, Zmax)
- Cephalexin (Keflex, Biocef, Keftab, etc.)
- Clotrimazole
- Doxycycline (Vibramycin, Doryx, Monodox, etc.
- Fluconazole (Diflucan)
- Itraconazole
- Ketoconazole
- Metronidazole (Acea, Anabact, Flagyl, etc.)
- Terbinafine (Lamisil)
- Other commonly prescribed medications for UTIs, strep, sinus infections, or sexually transmitted
Here is a list of commonly prescribed antibiotics that do interfere with the action of levonorgestrel type ECs. If you are taking any of these medications and need to use MAP or Plan B, talk to your doctor:
rifampin (Rifadin, Rimactane)
rifabutin (Mycobutin) used to treat tuberculosis,
According to research, they are potent enzyme inducers that can significantly reduce levonorgestrel's effectiveness. So, if you’ve taken rifampin or rifabutin recently, you will need to use an alternative EC product like Ella or a copper IUD.
HIV Medications
Certain HIV medications are enzyme inducers, meaning that they can reduce how well MAP and Plan B type ECs work in your body and make them less effective in delaying ovulation. The most significant are efavirenz (Sustiva, Stocrin), Rifampin (Rifadin, Rimactane) and rifabutin (Mycobutin).
If you’re taking any of these medications for your HIV treatment, the preferred effective emergency contraceptive options are Ella or the copper IUD. If you’re not sure which route to take, a healthcare provider or pharmacist can assist.
Anti-Tuberculosis Medications
Certain anti-tuberculosis medications are enzyme inducers too, meaning that they can reduce how well MAP and Plan B type ECs work in your body and make them less effective in delaying ovulation. The most significant are Rifampin (Rifadin, Rimactane) and rifabutin (Mycobutin).
If you’re taking any of these medications for your anti-tuberculosis treatment, the preferred effective emergency contraceptive options are Ella or the copper IUD. If you’re not sure which route to take, a healthcare provider or pharmacist can assist.
Herbal Supplements (e.g., St. John’s Wort)
While we’ve extensively discussed Plan B's effectiveness with other medications, we can’t forget herbal supplements. If you’re taking St. John’s Wort any levonorgestrel containing emergency contraceptives like MAP and Plan B are off limits. St John’s Wort really damages their effectiveness.
St. John’s Wort ramps up those same liver enzymes that clear levonorgestrel from the body. That means the morning-after pill won’t stick around long enough to be reliable. Even if you don’t take the herbal supplement regularly, it still lowers the effectiveness.
How do these Medications and Supplements Affect the Morning After Pill?
Without getting too science-y on you, here’s a brief overview of how morning-after pill drug interactions can occur:
Your liver plays a big role in how drugs are metabolized in your body. Picture a factory conveyor belt moving steadily. When certain medications speed up that belt, levonorgestrel races through the system and leaves before it can do what it needs to do.
This process, known as enzyme induction, is primarily driven by enzymes with Star Wars-like names such as CYP3A4. When these enzymes ramp up, they clear levonorgestrel faster than expected. For this reason it is advisable to use an alternative emergency contraceptive when taking medications or supplements that speed up the clearance of levonorgestrel used in Morning after Pill and Plan B type emergency contraceptives.
Certain medications, such as anticonvulsants, some antibiotics, and St. John’s Wort are known to cause drug interactions, including enzyme induction.
Enzyme induction can linger after stopping the medication. That’s why it’s super helpful to consider your regular prescriptions or supplements when choosing an emergency contraceptive.
If you are using other medications when you are thinking about using Morning after Pill or Plan B, check online to make sure that they will not impair the work of levonorgestrel and if it does, consider using an alternative emergency contraceptive like Ella or a copper IUD.
Learn more about how to use emergency contraception safely and effectively.
What to Do If You’re Taking Interacting Medications
If you found one or more of your medications or supplements on this list, don’t freak out; you still have several options you can explore outside of MAP & Plan B similar ECs.Here’s what you can do:
- Consider Ella: Ella works a bit differently from Plan B and isn’t affected by enzyme inducers to the same extent. It’s also more effective for people with a higher body weight and works up to five days after having unprotected sex.
- Get a copper IUD inserted by a qualified health professional: This device, which a healthcare provider must insert, can prevent pregnancy up to five days after unprotected sex, and works regardless of your body weight or medications. Bonus: you can leave it in and get long-term birth control if you wish.
- Speak with a pharmacist or healthcare provider: When you’re feeling unsure about the best route for your health and lifestyle, your best bet is to speak to a healthcare professional. A pharmacist or primary care provider can guide you through which option will work best based on what medications you’re taking.
- Avoid doubling up on Plan B: As tempting as it might be to double-dose, please don’t do it. Taking two Plan B pills doesn’t “cancel” out a drug interaction. Doing so won’t cause any harm, but it also won’t fix the enzyme induction issue.
Are There Any Medications That Make Plan B Unsafe?
There are no known medications that make MAP, Plan B or its generics unsafe to take. The concern is more about effectiveness than danger. So even if you’re unsure whether one of your medications interacts with Plan B, it’s not unsafe to take the emergency contraceptive pill. it’s best to err on the side of caution and use an alternative emergency contraceptive.
Why Understanding Interactions Matters
When it comes to emergency contraception, knowledge is power, not pressure. Understanding Plan B's effectiveness alongside other medications means you can make the best choices for your body and peace of mind.
It helps:
- Avoid surprises
- Choose the most effective emergency contraception
- Feel confident in your decision
- Stay prepared for whatever life throws at you
At Cadence OTC, we’re committed to giving you clear, evidence-backed information so you can protect yourself with zero shame and zero guesswork.
Order the Morning After Pill directly from Cadence OTC.
FAQs About Plan B Interactions
Still have a few questions about drug interactions Morning After Pill or Plan B and drug interactions? Hopefully, we’ll answer them below:
Does Topamax make Morning After Pill less effective?
Yes. Topamax is an enzyme inducer, which means Morning After Pill, Plan B and generics are broken down too fast to work correctly. Choosing another form of emergency contraception, such as Ella or a copper IUD, will give you much better protection.
Can antibiotics cancel out Plan B?
Two antibiotics can completely cancel out Morning After Pill and Plan B’s effectiveness. They are rifampin and rifabutin, both used to treat tuberculosis. Common antibiotics, such as amoxicillin and doxycycline, won’t interfere with the emergency contraceptive pill.
Is St. John’s Wort safe with Plan B?
Yes, it is physically safe to take St. John’s Wort with Plan B. However, it can reduce the effectiveness of the morning-after pill because it speeds up the metabolism of levonorgestrel. If you take St. John’s Wort, you will need an alternative emergency contraceptive, such as Ella or a copper IUD, for the best protection.
What are my options if I’m on seizure meds?
If you’re taking anti-seizure medications, such as Topamax or carbamazepine, choosing Ella or a copper IUD will be a more effective options compared to Morning After Pill and Plan B.
Conclusion
Plan B and other levonorgestrel-based morning-after pills are safe, effective, and accessible options for most people. But like anything we put in our bodies, they don’t exist in a vacuum. Certain medications and supplements clear out the hormone faster than normal, lowering its ability to prevent pregnancy.
It can be a bit of a bummer to know that drug interactions can occur with Morning After Pill and Plan B. Still, the good news is that once you understand what affects the morning-after pill (and what doesn’t), emergency contraception becomes way less confusing and can be used with confidence.
Being prepared is actually a good form of self-care. Whether you keep a morning-after pill in your bag or nightstand in case of a “whoopsie,” bookmark resources for later, or talk to your pharmacist or healthcare provider about your medications, you’re taking charge of your reproductive health with clarity rather than guesswork, and that’s something you deserve every time.
Learn more about safe, effective emergency contraception with Cadence OTC.
