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

If you're taking medication for seizures and also using birth control pills, patches, or the vaginal ring, there's a serious risk you're not protected against pregnancy-even if you take your pills every day without fail. This isn't a rare edge case. It's a well-documented, clinically significant drug interaction that affects hundreds of thousands of women worldwide. The problem? Certain seizure medications can make your birth control completely ineffective by speeding up how fast your body breaks down the hormones. And most women don’t even know it’s happening.

Which Anticonvulsants Kill Birth Control Effectiveness?

Not all seizure medications do this. But the ones that do are some of the most commonly prescribed. If you're taking carbamazepine (Tegretol), oxcarbazepine (Trileptal), phenytoin (Dilantin), phenobarbital, primidone (Mysoline), felbamate (Felbatol), or topiramate (Topamax) at doses above 200 mg/day, your birth control is likely being metabolized too fast to work. These drugs are called enzyme-inducing antiepileptic drugs (EIAEDs). They turn on liver enzymes-specifically CYP450-that break down estrogen and progestin before they can do their job. Studies show these medications can slash ethinyl estradiol (the estrogen in most pills) by 15% to 60%. Progestin levels drop even more-up to 50%. That’s not a small change. That’s enough to make your birth control useless. In fact, the FDA requires drug labels for carbamazepine to state clearly: "Contraceptives containing estrogen or progestin may be ineffective when used concurrently with Tegretol." Topiramate is especially tricky because the effect gets worse as the dose goes up. At 200 mg/day, estrogen levels drop 23%. At 400 mg/day? They drop 43%. That’s not a typo. That’s science.

What About Lamotrigine? It’s the Opposite Problem

Lamotrigine (Lamictal) doesn’t speed up hormone breakdown. Instead, it gets broken down faster by estrogen. Women taking combined oral contraceptives (pills with estrogen and progestin) see their lamotrigine levels drop by about 50%. That’s dangerous. Lamotrigine controls seizures. If your level drops too low, you could have a seizure you didn’t have before. And when you stop taking the pill-like during your sugar pill week-your lamotrigine level spikes back up. That 30-40% rebound can cause dizziness, blurred vision, or worse: a skin rash that could turn into a life-threatening condition called Stevens-Johnson syndrome. So if you’re on lamotrigine, estrogen-containing birth control is risky for both sides: it can cause seizures and serious side effects.

Which Birth Control Methods Still Work?

Not all birth control fails here. Some methods bypass the liver entirely or use doses so high that enzyme induction can’t overcome them.

• Progestin-only IUDs (Mirena, Kyleena, Liletta): These work locally in the uterus. Less than 0.1% of women using them get pregnant-even with enzyme-inducing anticonvulsants.
• Copper IUD (ParaGard): No hormones at all. It works by creating inflammation that kills sperm. Completely unaffected by any medication.
• Depo-Provera (DMPA): The shot gives you 150 mg of progestin every 12 weeks. That’s so much hormone that even accelerated metabolism can’t clear it fast enough. It remains effective.

These are the safest options. The American College of Obstetricians and Gynecologists (ACOG) recommends them as first-line choices for women on enzyme-inducing anticonvulsants.

What About the Patch, Ring, and Pill?

The patch (Ortho Evra) and the ring (NuvaRing) are just as risky as the pill. They deliver estrogen and progestin through the skin or vagina, but those hormones still go to the liver. Once there, enzyme-inducing drugs like carbamazepine shred them. Even high-dose pills (50 mcg ethinyl estradiol) aren’t reliable enough. The Epilepsy Foundation says even these can fail. And many women don’t even know they’re on a low-dose pill. Most brands today have 20-30 mcg-far too low to overcome enzyme induction.

Emergency Contraception? Don’t Rely on It

If you have unprotected sex while on an enzyme-inducing anticonvulsant, Plan B (levonorgestrel) might not work. Studies show its effectiveness drops by about 50%. Ella (ulipristal acetate) may also be less effective. That means emergency contraception isn’t a backup plan here-it’s a gamble. If you need it, talk to your doctor immediately. You might need a higher dose or a copper IUD inserted as emergency contraception.

Why Do So Many Women Get Pregnant Without Knowing?

A 2022 survey by the Epilepsy Foundation found only 35% of women with epilepsy got counseling from their neurologist about birth control. Only 22% heard it from their gynecologist. It’s not that doctors are careless. Many don’t know the full picture. But the data is clear: women on carbamazepine or topiramate are 2-3 times more likely to have an unintended pregnancy than women not on these drugs. Reddit threads are full of stories like this: "I got pregnant on Ortho Tri-Cyclen while taking Tegretol despite perfect use-my neurologist never warned me." Another wrote: "I had two miscarriages before I found out my birth control didn’t work with my meds. No one told me."

What Should You Do?

If you’re on one of these seizure meds and using birth control:

1. Check what kind of anticonvulsant you’re taking. Is it carbamazepine, topiramate, phenytoin, or another enzyme inducer?
2. Check your birth control. Are you on a pill, patch, or ring? If yes, you’re at high risk.
3. Don’t assume your doctor told you. Ask directly: "Do my seizure meds interfere with my birth control?" If they say "probably not," ask for proof.
4. Switch to an IUD or Depo-Provera. These are proven safe. No guesswork.
5. If you must stay on hormonal birth control, use condoms every time. Double protection is better than none.

What About Newer Seizure Meds?

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, patch, or ring should work fine. Even newer drugs like perampanel (Fycompa) and brivaracetam (Briviact) show little to no enzyme induction. They’re becoming preferred choices for women who need both seizure control and reliable contraception.

What If You’re Trying to Get Pregnant?

If you’re planning pregnancy, this isn’t just about birth control. It’s about safety. Enzyme-inducing anticonvulsants like carbamazepine and phenytoin increase the risk of major birth defects by 30-40% compared to the general population’s 2-3%. That’s why preconception counseling is critical. Talk to both your neurologist and OB-GYN before stopping birth control. You may need to switch to a safer seizure medication months before trying to conceive. Folic acid (at least 4 mg/day) is also strongly recommended.

Bottom Line

This isn’t a "maybe" or a "might." This is a proven, dangerous interaction that’s been known since the 1970s. Women are still getting pregnant because no one told them. If you’re on carbamazepine, topiramate, phenytoin, or another enzyme-inducing anticonvulsant, your birth control pill, patch, or ring is likely not working. Don’t risk it. Switch to an IUD or Depo-Provera. Ask your doctor for help. Your body deserves better than guesswork.