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 rare issue-it’s a well-documented, clinically significant interaction that puts thousands of women at risk for unintended pregnancy every year. If you’re on medications like carbamazepine, oxcarbazepine, or topiramate, and you’re using the pill, patch, or ring, your contraception could be failing without you knowing it.

How Anticonvulsants Break Down Birth Control

The problem starts in your liver. Certain anticonvulsants trigger enzymes called cytochrome P450, 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 are metabolized too quickly, they never reach the concentration needed to work.

Studies show that enzyme-inducing anticonvulsants can drop estrogen levels by 15% to 60% and progestin by 20% to 50%. That’s not a small drop-it’s enough to let ovulation happen. For example, women taking topiramate at 400 mg per day saw estrogen levels fall by 43%. At that point, the pill becomes unreliable, even if taken perfectly.

Which Anticonvulsants Are the Worst Offenders?

Not all seizure medications affect birth control the same way. Some are high-risk. Others are safe. Here’s the breakdown:

• High risk (strong enzyme inducers): Carbamazepine (Tegretol), oxcarbazepine (Trileptal), phenytoin (Dilantin), phenobarbital, primidone (Mysoline), felbamate (Felbatol), and topiramate (Topamax) at doses over 200 mg/day.
• Unique interaction: Lamotrigine (Lamictal) doesn’t speed up hormone breakdown-but birth control pills cut lamotrigine levels by half. That increases seizure risk. Plus, when you stop taking the pill during your placebo week, lamotrigine spikes, which can cause dizziness, blurred vision, or even seizures.
• Safe options: Valproate (Depakote), gabapentin (Neurontin), pregabalin (Lyrica), and levetiracetam (Keppra) don’t interfere with hormonal birth control.

The FDA requires drug labels to warn about these interactions. The Tegretol package insert says plainly: “Contraceptives containing estrogen or progestin may be ineffective when used concurrently with Tegretol.” If your doctor didn’t mention this, they’re not up to date.

What Birth Control Methods Still Work?

If you’re on a high-risk anticonvulsant, your options aren’t gone-they just need to change. Here’s what works:

• Levonorgestrel IUDs (Mirena, Kyleena): These release progestin directly into the uterus. Blood levels stay high enough to prevent pregnancy even with enzyme inducers. Pregnancy rates are under 0.1% per year.
• Copper IUD (ParaGard): No hormones at all. Works by creating an inflammatory reaction that stops 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 metabolism can’t break it down fast enough to cause failure.
• Progestin-only pill (minipill): May work if taken perfectly every day, but it’s not ideal. Missing a pill by even 3 hours can reduce effectiveness. Most experts don’t recommend it as a first choice here.

What doesn’t work? The pill, patch, and ring. Even if you take them perfectly, the drugs are still breaking down the hormones too fast. Emergency contraception is also risky. Plan B (levonorgestrel) loses about half its effectiveness. Ella (ulipristal acetate) may not work at all. If you need emergency contraception, go straight to a copper IUD inserted within 5 days-it’s the only reliable option.

What About Lamotrigine and Birth Control?

This is a tricky one. Lamotrigine is often the go-to drug for women with epilepsy because it has fewer side effects and less risk to a developing baby. But it’s caught in the middle.

Combined hormonal birth control cuts lamotrigine levels by about 50%. That means your seizure control could slip. One woman on Reddit shared: “I had two seizures in a week after starting the pill. My neurologist didn’t know the pill would lower my lamotrigine.”

The fix? Either avoid estrogen entirely and use a progestin-only method, or adjust your lamotrigine dose. Most doctors increase the dose by 50-100% when someone starts hormonal birth control. But you need close monitoring-blood tests every few weeks-to make sure you’re in the safe range. Avoid the placebo week in your pill pack. Extended-cycle pills (taking active pills for 84 days straight) help keep lamotrigine levels stable.

Why This Isn’t Just About Pregnancy

Unplanned pregnancy is dangerous for women on anticonvulsants. Many seizure medications-especially enzyme inducers-carry a 30-40% higher risk of major birth defects compared to the general population’s 2-3%. That includes heart defects, cleft palate, and neural tube defects.

Plus, pregnancy can make seizures worse. Hormonal shifts, sleep disruption, and stress all trigger seizures. If you’re not planning to get pregnant, you’re not just protecting yourself-you’re protecting a future child.

Why So Many Women Don’t Know This

A 2022 survey by the Epilepsy Foundation found that only 35% of women with epilepsy got counseling about birth control interactions from their neurologist. Only 22% heard it from their gynecologist. That’s a massive gap.

One woman wrote in a support group: “I got pregnant on Ortho Tri-Cyclen while taking Tegretol. My neurologist never mentioned it. My OB said the pill was fine. No one connected the dots.”

This isn’t just a lack of communication-it’s a systemic failure. Neurologists focus on seizure control. Gynecologists focus on contraception. Neither always checks what the other is prescribing.

What You Should Do Right Now

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

1. Identify your medication. Is it carbamazepine, topiramate, phenytoin, or lamotrigine? If yes, you’re at risk.
2. Check your current method. Are you using the pill, patch, or ring? If yes, stop relying on it.
3. See both your neurologist and gynecologist. Bring this article. Ask: “Does my medication interfere with my birth control? What’s the safest option for me?”
4. Choose a non-interfering method. Go for a levonorgestrel IUD or copper IUD. They’re long-lasting, over 99% effective, and require no daily effort.
5. Use backup protection. If you’re still on a risky method, use condoms every time until you switch.

Don’t wait for your next appointment. If you’re sexually active and on one of these drugs, your birth control might already be failing. You don’t need to guess. You don’t need to hope. You just need to act.

What’s Changing in 2025?

Newer anticonvulsants like perampanel (Fycompa) and brivaracetam (Briviact) don’t induce liver enzymes. That means they’re safer for women who need reliable contraception. More doctors are switching patients to these drugs when possible.

The NIH is tracking 5,000 pregnancies to better understand how different anticonvulsants affect birth outcomes. And the Bill & Melinda Gates Foundation is funding a non-hormonal contraceptive gel that works without touching liver metabolism-potentially solving this problem for good.

In early 2024, the American College of Obstetricians and Gynecologists and the American Academy of Neurology are launching a shared decision-making toolkit for doctors. It’s designed to make sure no woman slips through the cracks again.

For now, the solution is simple: Know your drugs. Know your options. Don’t assume your birth control is working. And don’t let silence put your health at risk.