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

It’s not just about taking your pills on time. If you’re on anticonvulsants for epilepsy or another seizure disorder and using birth control pills, the patch, or the ring, your contraception might not be working like you think. This isn’t a myth or a rare edge case-it’s a well-documented, clinically significant interaction that puts thousands of women at risk of unintended pregnancy every year.

Why Your Birth Control Might Be Failing

The problem starts in your liver. Certain anticonvulsants-like carbamazepine (Tegretol), phenytoin (Dilantin), oxcarbazepine (Trileptal), and topiramate (Topamax)-trigger your liver to produce more enzymes that break down hormones. These are called enzyme-inducing antiepileptic drugs (EIAEDs). They don’t just speed up how fast your body processes the seizure meds themselves-they also speed up how fast it breaks down estrogen and progestin, the key hormones in most birth control methods.

Studies show these drugs can slash ethinyl estradiol levels by up to 60% and progestin levels by half. That’s not a small drop. That’s enough to turn a highly effective contraceptive into a unreliable one. The result? Breakthrough bleeding, missed periods, and, most dangerously, unplanned pregnancy.

One 2019 study of 327 women with epilepsy found that 42% had breakthrough bleeding while on birth control pills alongside enzyme-inducing anticonvulsants. And 18% had at least one unintended pregnancy-even when they took their pills exactly as directed. This isn’t about user error. It’s about chemistry.

Which Anticonvulsants Are the Biggest Culprits?

Not all seizure medications affect birth control the same way. Here’s the clear breakdown:

• High risk: Carbamazepine, oxcarbazepine, phenytoin, phenobarbital, primidone, topiramate (especially at doses over 200 mg/day), and felbamate. These strongly activate liver enzymes and cut hormone levels dramatically.
• Unique risk: Lamotrigine doesn’t speed up hormone breakdown, but it’s the opposite: your birth control speeds up its breakdown. If you’re on lamotrigine and take combined hormonal contraceptives, your lamotrigine levels can drop by 50%. That means your seizures could get worse. And when you stop taking the pill during your placebo week, lamotrigine levels spike-raising your risk of dizziness, blurred vision, or even more seizures.
• Low to no risk: Valproate (Depakote), gabapentin (Neurontin), pregabalin (Lyrica), and levetiracetam (Keppra). These don’t interfere with hormonal birth control and are safer choices if you’re trying to get pregnant or avoid it.

Even if your doctor says your seizure meds are "safe," always double-check. Many patients assume if their neurologist didn’t mention it, it’s not a problem. But a 2022 survey by the Epilepsy Foundation found only 22% of women were counseled by their gynecologist about this interaction, and just 35% by their neurologist.

What Birth Control Methods Actually Work?

If you’re on one of the high-risk anticonvulsants, your options narrow-but they’re still there. Here’s what works, and what doesn’t:

• Don’t rely on: Combined oral contraceptives (the pill), the patch (Ortho Evra), or the vaginal ring (NuvaRing). All rely on hormones your liver will break down too fast.
• Safe and effective: The copper IUD (ParaGard). It works without hormones, so anticonvulsants have zero effect on it. Pregnancy rate? Less than 0.1% per year.
• Also safe: Levonorgestrel IUDs like Mirena and Kyleena. Even with enzyme-inducing drugs, these remain over 99% effective. The hormone is delivered directly into the uterus, bypassing the liver’s metabolism.
• Safe: Depo-Provera (the shot). The high dose of progestin (150 mg every 12-13 weeks) overwhelms the liver’s ability to break it down, so it still works.
• Unreliable: Emergency contraception. Levonorgestrel (Plan B) is about 50% less effective if you’re on enzyme-inducing drugs. Ulipristal acetate (Ella) may not work at all. If you need emergency contraception, the copper IUD is the gold standard-it’s more effective than any pill and can stay in place as long-term birth control.

Some doctors suggest using birth control pills with 50 mcg or more of ethinyl estradiol to counteract the interaction. But even that’s not foolproof. The CDC classifies combined hormonal contraceptives as Category 3 for women on enzyme-inducing anticonvulsants-meaning the risks usually outweigh the benefits.

Lamotrigine and Birth Control: A Two-Way Street

Lamotrigine is tricky. It doesn’t make birth control fail-but birth control makes lamotrigine fail. If you’re on lamotrigine and start the pill, your seizure control could slip. That’s dangerous. Seizures during pregnancy carry higher risks for both mother and baby, including injury and preterm birth.

Women on lamotrigine who need hormonal contraception have a few options:

• Switch to a non-estrogen method like the IUD or the shot.
• If you must use estrogen-containing birth control, your doctor may need to increase your lamotrigine dose by 50-100%. But this requires close monitoring-blood tests every few weeks to make sure levels are right.
• Use extended-cycle pills (skipping the placebo week) to avoid the hormone dip that causes lamotrigine spikes.

One woman on Reddit shared: "I got pregnant on Ortho Tri-Cyclen while taking Tegretol despite perfect use-my neurologist never warned me." That story isn’t rare. And it’s preventable.

What Should You Do?

If you’re taking anticonvulsants and need birth control, here’s your action plan:

1. Ask your neurologist: "Is my seizure medication an enzyme inducer?" If yes, you need to rethink your birth control.
2. See your gynecologist or a reproductive health specialist. Bring your full medication list. Don’t assume they know about neurology drug interactions.
3. Choose a non-hormonal method if possible. The copper IUD is the most reliable option.
4. If you choose a hormonal method, use a backup barrier method like condoms every time-especially if you’re on topiramate, carbamazepine, or phenytoin.
5. Never start or stop birth control without talking to both your neurologist and your gynecologist. This isn’t a one-time conversation-it needs to be revisited if your seizure meds change.

And if you’re planning to get pregnant? Talk to your doctors before you stop birth control. Some anticonvulsants increase the risk of birth defects by 30-40%. Planning ahead lets you switch to safer medications before conception.

The Bigger Picture

About 2.3 million women of childbearing age in the U.S. take anticonvulsants. Over 70% are in their reproductive years. That’s a huge population with a hidden risk. Unplanned pregnancies in this group happen at rates as high as 50%-far above the general population. And it’s not because women aren’t trying. It’s because the system isn’t communicating.

Drug manufacturers know. The Tegretol package insert says plainly: "Contraceptives containing estrogen or progestin may be ineffective when used concurrently with Tegretol." But many patients never see that label. Doctors don’t always bring it up. And women are left guessing.

Newer anticonvulsants like perampanel (Fycompa) and brivaracetam (Briviact) have minimal enzyme-inducing effects. That’s good news. But they’re not yet the first-line choice for everyone. And many women are still stuck on older, cheaper meds that come with this risk.

There’s hope. The NIH is tracking 5,000 pregnancies to better understand these interactions. The Gates Foundation is funding research into non-hormonal contraceptive gels that could bypass this problem entirely. And ACOG and the American Academy of Neurology are releasing a shared decision-making toolkit for doctors in early 2024.

But right now, the responsibility falls on you. Don’t wait for your doctor to bring it up. Ask. Push. Get tested. Choose wisely. Your birth control isn’t failing because you forgot a pill. It’s failing because of chemistry you can’t control-unless you know how to work around it.