Anticonvulsants and Birth Control: What You Need to Know About Reduced Effectiveness

Many women taking anticonvulsants for epilepsy or other seizure disorders don’t realize their birth control might not be working as expected. This isn’t a myth or a rare edge case-it’s a well-documented, clinically significant interaction that affects over 1.2 million women in the U.S. alone. If you’re on carbamazepine, phenytoin, topiramate, or similar medications and using the pill, patch, or ring, you could be at risk for unintended pregnancy-even if you take your birth control perfectly.

How Anticonvulsants Break Down Birth Control

The problem starts in your liver. Certain anticonvulsants trigger enzymes called cytochrome P450 (CYP450), which speed up how fast your body breaks down hormones. Oral contraceptives rely on steady levels of estrogen and progestin to prevent ovulation. When these hormones get metabolized too quickly, they never reach the concentration needed to work.

It’s not just a little less effective-it’s a big drop. Studies show that ethinyl estradiol (the estrogen in most pills) can drop by 15% to 60% when taken with enzyme-inducing anticonvulsants. Progestin levels can fall by 20% to 50%. That’s enough to stop ovulation from being blocked, which means pregnancy becomes possible.

This isn’t guesswork. It’s been known since the 1970s. Back then, doctors noticed women on both seizure meds and birth control were having breakthrough bleeding and unexpected pregnancies. Today, we have the science to explain why: the liver enzymes are working overtime, turning active hormones into inactive waste before they can do their job.

Which Anticonvulsants Are the Problem?

Not all seizure medications mess with birth control. Some do. Others don’t. Here’s the breakdown:

• High risk: Carbamazepine (Tegretol), oxcarbazepine (Trileptal), topiramate (Topamax), phenytoin (Dilantin), phenobarbital, primidone (Mysoline), felbamate (Felbatol)
• Unique risk: Lamotrigine (Lamictal)-it doesn’t speed up hormone breakdown, but hormonal birth control slashes lamotrigine levels by about 50%. That raises your seizure risk. Plus, when you take your pill-free week, lamotrigine spikes, which can cause dizziness, headaches, or even seizures.
• Safe: Valproate (Depakote), gabapentin (Neurontin), pregabalin (Lyrica), levetiracetam (Keppra)

If you’re on lamotrigine, estrogen-containing birth control is especially dangerous-not because it fails, but because it makes your seizure control worse. That’s a double threat: higher chance of unplanned pregnancy and higher chance of seizures.

What Birth Control Methods Still Work?

Not all hope is lost. Some forms of birth control bypass the liver entirely or use doses too high for the enzymes to overwhelm.

• Levonorgestrel IUDs (Mirena, Kyleena): These release progestin directly into the uterus. Studies show pregnancy rates are under 0.1% per year, even with enzyme-inducing anticonvulsants.
• Copper IUD (ParaGard): No hormones at all. Works by creating a hostile environment for sperm. Completely unaffected by any medication.
• Depo-Provera (DMPA): The shot delivers 150 mg of progestin every 12-13 weeks. That’s such a high dose that liver enzymes can’t break it down fast enough to stop it from working.

These are the gold standard options for women on risky anticonvulsants. They’re long-lasting, reliable, and don’t require daily tracking. And unlike pills, they don’t rely on your liver to keep them active.

What Doesn’t Work Anymore

If you’re on carbamazepine, topiramate, or phenytoin, these methods are not safe as your only protection:

• Combined oral contraceptives (the pill): Even high-dose pills (50 mcg estrogen) are less effective. The FDA label for Tegretol literally says: “Contraceptives containing estrogen or progestin may be ineffective.”
• The patch (Ortho Evra): Though it delivers hormones through the skin, it still goes through the liver. Studies show it’s not reliable with enzyme inducers.
• The ring (NuvaRing): Same issue as the pill-hormones get broken down too fast.
• Emergency contraception: Plan B (levonorgestrel) loses about half its effectiveness. Ella (ulipristal) may not work at all. If you need emergency contraception and you’re on an enzyme-inducing drug, you need a copper IUD inserted within 5 days. That’s the only reliable option.

Real Stories, Real Risks

Behind the numbers are real people. A 2019 study of 327 women with epilepsy found that 42% had breakthrough bleeding while on birth control pills and anticonvulsants. 18% had an unplanned pregnancy-despite perfect pill use.

One Reddit user wrote: “I got pregnant on Ortho Tri-Cyclen while taking Tegretol. My neurologist never warned me.” Another shared: “After switching from pills to Mirena, my periods became regular and my seizures stayed under control.”

These aren’t outliers. They’re symptoms of a systemic gap. A 2022 survey by the Epilepsy Foundation found that only 35% of women with epilepsy received contraceptive counseling from their neurologist. Only 22% got it from their gynecologist. That’s a dangerous disconnect.

What Should You Do?

If you’re taking an anticonvulsant and using hormonal birth control, here’s your action plan:

1. Know your drug. Check if yours is an enzyme inducer. If you’re unsure, ask your pharmacist or look up the brand name with “drug interactions.”
2. Stop relying on pills, patches, or rings. Even if you’ve never had a problem, the risk is still there.
3. Switch to an IUD or shot. Mirena, Kyleena, or Depo-Provera are your safest bets.
4. If you’re on lamotrigine, avoid estrogen. Talk to your doctor about switching to a progestin-only IUD or adjusting your lamotrigine dose if you must use hormonal birth control.
5. Always use backup. If you’re on a risky anticonvulsant and using a hormonal method, add condoms. They’re not perfect, but they add a layer of protection.

What About Newer Medications?

There’s good news. Newer anticonvulsants like perampanel (Fycompa) and brivaracetam (Briviact) don’t trigger liver enzymes the same way. They’re becoming preferred choices for women of childbearing age who need both seizure control and reliable contraception.

The NIH is currently tracking 5,000 pregnancies to better understand how these newer drugs affect birth outcomes. And research is underway for non-hormonal contraceptives-like a gel being tested by the Gates Foundation-that could eliminate this whole problem.

Why This Matters Beyond Pregnancy

Unplanned pregnancy isn’t just inconvenient-it’s dangerous. Women with epilepsy who get pregnant while on enzyme-inducing anticonvulsants face a 30-40% higher risk of major birth defects compared to the general population. That’s not a small number. It’s why preventing unintended pregnancy isn’t just about birth control-it’s about protecting the health of the mother and the baby.

That’s why organizations like ACOG and the American Academy of Neurology are pushing for better collaboration between neurologists and OB-GYNs. A shared decision-making toolkit is launching in early 2024 to help doctors talk to patients clearly and consistently.

You don’t have to accept this risk. You don’t have to guess. There are safe, effective options. You just need to ask the right questions-and make sure your care team is listening.