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

Why Your Birth Control Might Not Be Working With Your Seizure Medication

If you’re taking medication for epilepsy or another seizure disorder and using birth control pills, the patch, or the ring, there’s a real chance your birth control isn’t working as well as you think. This isn’t a myth, a rare side effect, or a misunderstanding - it’s a well-documented, clinically significant interaction that affects hundreds of thousands of women in the U.S. every year. The problem? Certain anticonvulsants speed up how your body breaks down the hormones in birth control, leaving you unprotected without you even realizing it.

Which Anticonvulsants Are the Problem?

Not all seizure medications interfere with birth control. But the ones that do are common and powerful. Carbamazepine (Tegretol), phenytoin (Dilantin), phenobarbital, primidone, oxcarbazepine (Trileptal), and felbamate (Felbatol) are all strong enzyme inducers. They turn on liver enzymes - specifically the CYP450 system - that digest estrogen and progestin faster than normal. Studies show these drugs can slash estrogen levels by up to 60% and progestin by half. That’s enough to cause ovulation even when you take your pill at the same time every day.

Topiramate (Topamax) is another big one - but only at higher doses. At 200 mg per day, it cuts estrogen levels by 23%. At 400 mg, that jumps to 43%. If you’re on topiramate for migraines or weight loss and also using birth control, your doctor should know. Many people don’t realize topiramate is an anticonvulsant, even if they’re not using it for seizures.

What About Lamotrigine?

Lamotrigine (Lamictal) is different. It doesn’t speed up hormone breakdown. But your birth control speeds up its breakdown. Combined hormonal contraceptives can cut lamotrigine levels in half. That’s dangerous. If you’re on lamotrigine for seizure control, a drop in its concentration can mean more seizures - even if you’ve been stable for years. And when you stop taking the pill during your placebo week, lamotrigine levels spike again, raising the risk of dizziness, rash, or worse. This back-and-forth makes hormonal birth control a risky choice if you’re on lamotrigine.

Which Birth Control Methods Are Safe?

Not all birth control is created equal when it comes to drug interactions. Here’s what works - and what doesn’t.

• Don’t rely on: Combined oral contraceptives (the pill), the patch (Ortho Evra), or the ring (NuvaRing). All of these deliver estrogen and progestin that get broken down too fast by enzyme-inducing anticonvulsants.
• Safe options: The copper IUD (ParaGard) is completely unaffected. It doesn’t use hormones at all. It’s 99% effective and lasts up to 12 years.
• Also safe: Levonorgestrel IUDs like Mirena and Kyleena. Studies show pregnancy rates under 0.1% per year, even with carbamazepine or phenytoin.
• Safe for some: Depo-Provera (the shot). The high dose of progestin (150 mg every 12 weeks) overwhelms the liver’s ability to break it down. It’s a solid choice if you don’t want an IUD.
• Not reliable: Emergency contraception. Plan B (levonorgestrel) loses about half its effectiveness with enzyme-inducing drugs. Ella (ulipristal) may not work at all. If you need emergency contraception, talk to your doctor - a copper IUD inserted within five days is the most effective option.

What Do Experts Say?

The American College of Obstetricians and Gynecologists (ACOG) and the American Academy of Neurology both agree: if you’re on carbamazepine, phenytoin, or similar drugs, combined hormonal birth control is a Category 3 risk - meaning the risks usually outweigh the benefits. That doesn’t mean it’s banned, but it means you need to know the dangers and have a backup plan.

ACOG recommends using a barrier method - like condoms - along with hormonal birth control if you choose to use it. But even then, the failure rate is higher than you’d expect. Many women think they’re protected because they’ve never missed a pill. But this isn’t about user error. It’s about chemistry.

For women on lamotrigine, the advice is clearer: avoid estrogen-containing birth control. Use progestin-only methods like the IUD, the shot, or the implant. If you must use the pill, your doctor may need to increase your lamotrigine dose by 50-100% - but that requires careful blood level monitoring.

Real Stories, Real Risks

A 2019 study of 327 women with epilepsy found that 42% had breakthrough bleeding while on birth control with enzyme-inducing anticonvulsants. That’s a red flag. And 18% had at least one unintended pregnancy - even with 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 the pill to Mirena, my periods got regular and my seizures stayed under control.”

These aren’t outliers. A 2022 survey by the Epilepsy Foundation found that only 35% of women with epilepsy got counseling about birth control from their neurologist. Only 22% from their gynecologist. That’s a massive gap in care.

What About Newer Medications?

Good news: newer anticonvulsants like levetiracetam (Keppra), gabapentin (Neurontin), pregabalin (Lyrica), and valproate (Depakote) don’t interfere with birth control. If you’re on one of these, your pill should work fine.

Even newer drugs like perampanel (Fycompa) and brivaracetam (Briviact) show little to no enzyme-inducing activity. That makes them better options for women who need both seizure control and reliable contraception. Some doctors are now switching patients from carbamazepine to these newer drugs specifically to avoid birth control issues.

What Should You Do?

Here’s your action plan:

1. Know your meds. Write down every seizure medication you take. Look up if it’s an enzyme inducer. If you’re unsure, ask your pharmacist.
2. Don’t assume your doctor knows. If you’re seeing a neurologist for seizures and a gynecologist for birth control, they may not be talking to each other. Bring up the interaction yourself.
3. Choose a safe method. The copper IUD is the gold standard. Mirena or Kyleena are excellent alternatives. The shot works too.
4. If you must use the pill: Use the highest dose available (at least 50 mcg ethinyl estradiol) and always use condoms. Track your cycle closely. If you have breakthrough bleeding, it’s a warning sign.
5. Ask about lamotrigine. If you’re on lamotrigine, avoid estrogen. Talk to your doctor about adjusting your dose if you switch to hormonal birth control.
6. Emergency contraception isn’t reliable. If you’ve had unprotected sex, get a copper IUD inserted within five days. It’s the most effective option.

Why This Matters Beyond Pregnancy

Unplanned pregnancy isn’t just inconvenient - it’s dangerous if you’re on enzyme-inducing anticonvulsants. These drugs carry a 30-40% higher risk of major birth defects compared to the general population. That’s why preventing pregnancy isn’t just about avoiding an unplanned child - it’s about protecting the health of a future baby.

And if you do become pregnant, stopping your seizure meds suddenly can be just as risky. Seizures during pregnancy can lead to miscarriage, preterm labor, or fetal injury. That’s why planning ahead - not reacting after a missed period - is critical.

The Bottom Line

If you’re taking carbamazepine, phenytoin, topiramate, or similar seizure meds, your birth control pill, patch, or ring might not be working. That’s not your fault. It’s a hidden drug interaction that’s been known for decades - but still isn’t talked about enough.

The safest path? Talk to both your neurologist and your gynecologist. Get an IUD. Or use the shot. Don’t rely on pills alone. And if you’re on lamotrigine, skip estrogen entirely. You don’t need to choose between controlling your seizures and preventing pregnancy. You just need the right information - and the right method.