Anticonvulsants and Oral Contraceptives: How Seizure Medications Can Reduce Birth Control Effectiveness

When you’re taking medication for seizures, the last thing you should worry about is getting pregnant accidentally. But for women using certain anticonvulsants along with oral contraceptives, that risk is real-and it’s not rare. This isn’t a myth or a footnote in a medical textbook. It’s a documented, well-studied interaction that has led to thousands of unintended pregnancies. And many women don’t even know it’s happening.

Why Some Seizure Medications Break Birth Control

The problem isn’t with birth control pills themselves. It’s with how your body processes them when you’re also taking certain anticonvulsants. Some seizure drugs, like carbamazepine (Tegretol), phenytoin (Dilantin), and topiramate (Topamax), trigger your liver to speed up the breakdown of hormones. These drugs activate enzymes called cytochrome P450, which turn estrogen and progestin into inactive waste products before your body can use them to prevent ovulation.

That means even if you take your pill at the same time every day, your hormone levels might drop too low to work. Studies show ethinyl estradiol (the estrogen in most pills) can be reduced by up to 60%. Progestin levels can drop by half. For women on high doses of topiramate (400 mg/day), estrogen levels fall by 43%. That’s not a small drop-it’s enough to make birth control unreliable.

Which Anticonvulsants Are the Biggest Risk?

Not all seizure medications do this. Some are safe. Others are dangerous. Here’s the split:

• High risk: Carbamazepine, oxcarbazepine, phenytoin, phenobarbital, primidone, topiramate (especially over 200 mg/day), and felbamate. These are strong enzyme inducers and should be treated as red flags.
• Unique risk: Lamotrigine doesn’t speed up hormone breakdown, but it’s the opposite: birth control pills reduce lamotrigine levels by about 50%. That means your seizure control could weaken, and you might have more seizures. Plus, when you stop taking the pill (during your placebo week), lamotrigine spikes back up-raising your risk of dizziness, rashes, or even seizures.
• Safe options: Valproate, gabapentin, pregabalin, and levetiracetam (Keppra). These don’t interfere with hormones. If you’re on one of these, your birth control should work as expected.

The difference matters. If you’re on carbamazepine and a regular pill, your chance of pregnancy is significantly higher than someone on levetiracetam. Yet, a 2022 survey found only 22% of women with epilepsy were told about this by their gynecologist. And only 35% heard it from their neurologist.

What Birth Control Methods Actually Work?

If you’re on an enzyme-inducing anticonvulsant, your best options aren’t the ones you might assume.

• Don’t rely on: Combined oral contraceptives, the patch (Ortho Evra), or the vaginal ring (NuvaRing). All of these rely on hormones your liver will break down too fast.
• Safe and effective: The Mirena or Kyleena IUD (both contain levonorgestrel). Studies show pregnancy rates under 0.1% per year-even with carbamazepine or topiramate. The copper IUD (ParaGard) works too, and it’s completely hormone-free.
• Also safe: The Depo-Provera shot. It delivers a high dose of progestin directly into your muscle, bypassing the liver’s first-pass metabolism. It’s still effective.
• Emergency contraception? Be careful. Plan B (levonorgestrel) may be half as effective. Ella (ulipristal) might not work at all. If you need emergency contraception, talk to your doctor immediately. A copper IUD inserted within 5 days is the most reliable option.

One woman on Reddit shared: “I got pregnant on Ortho Tri-Cyclen while taking Tegretol-even though I never missed a pill.” Her neurologist never mentioned the risk. She’s not alone. A 2019 study of 327 women with epilepsy found 18% had an unintended pregnancy while on hormonal birth control.

What About Lamotrigine and Birth Control?

Lamotrigine is tricky. It doesn’t break down birth control-but birth control breaks down lamotrigine. That’s a two-way street.

If you’re on lamotrigine and start a pill, your seizure control could get worse. Your doctor might need to increase your lamotrigine dose by 50-100% to compensate. But then, when you take your placebo week, your lamotrigine level shoots back up. That can cause side effects like dizziness, blurred vision, or worse-seizures.

The safest approach? Avoid estrogen-containing birth control entirely. Use a progestin-only IUD or shot. If you must use a pill, your doctor might recommend an extended-cycle pill (no placebo week) to keep lamotrigine levels stable. But this requires close monitoring.

What Do Doctors Say?

Major medical groups are clear:

• The American College of Obstetricians and Gynecologists (ACOG) says combined hormonal birth control is not recommended for women on enzyme-inducing anticonvulsants. They classify it as “Category 3”-theoretical or proven risks usually outweigh the benefits.
• The American Academy of Neurology and the American Epilepsy Society warn that estrogen-containing contraceptives can make lamotrigine less effective, increasing seizure risk.
• The CDC agrees: combined pills are a risky choice for this group.

Dr. Hadine Joffe from Massachusetts General Hospital points out: “The patch isn’t metabolized the same way as pills, so it might be a better option.” But even that’s not a guarantee. The safest advice? Use a non-hormonal method.

Why This Matters More Than You Think

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. Seizures during pregnancy can also harm both mother and baby.

And it’s not just about pregnancy. Many women experience breakthrough bleeding-spotting or irregular periods-when these drugs interact. That’s often the first warning sign that birth control isn’t working. But too many women think it’s just a side effect, not a red flag.

What Should You Do?

If you’re taking any anticonvulsant and using hormonal birth control, here’s what to do now:

1. Know your drug. Is it carbamazepine, topiramate, phenytoin? If yes, assume your birth control is compromised.
2. Don’t assume your doctor told you. Only 22% of women heard this from their gynecologist. Ask directly: “Does my seizure medication affect my birth control?”
3. Switch to a safer method. The Mirena or Kyleena IUD is the top recommendation. The copper IUD is the safest. The Depo shot is also reliable.
4. If you’re on lamotrigine, avoid estrogen. Talk to your neurologist about dose adjustments if you must use hormonal birth control.
5. Use condoms as backup. Even if you’re on an IUD, condoms add protection and prevent STIs.

There’s no shame in switching. In fact, it’s smart. One woman wrote on a Planned Parenthood forum: “After switching from pills to Mirena when I started Keppra, my periods became regular and I haven’t had any seizure changes.” That’s the outcome everyone wants.

The Future Is Changing

Newer seizure drugs like perampanel (Fycompa) and brivaracetam (Briviact) don’t interfere with hormones. More doctors are switching patients to these when possible. And research is underway for non-hormonal contraceptives-like a gel being tested by the Gates Foundation-that could eliminate this problem entirely.

But right now, the solution is simple: know your drugs, know your options, and talk to both your neurologist and your gynecologist. Don’t wait for a surprise pregnancy. This interaction is predictable, preventable, and well-documented. You deserve to be in control.