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

If you're taking medication for seizures and also using birth control pills, patches, or rings, there's a real chance your birth control isn't working as well as you think. This isn't a rare issue - it's a well-documented, dangerous interaction that affects over a million women in the U.S. alone. Many women don't even know it's happening until they get pregnant - despite using birth control perfectly. The problem isn't user error. It's a hidden drug interaction between anticonvulsants and hormones.

Which Anticonvulsants Lower Birth Control Effectiveness?

Not all seizure medications cause this problem. Only the ones that boost liver enzymes do. These are called enzyme-inducing antiepileptic drugs (EIAEDs). They speed up how fast your body breaks down estrogen and progestin - the hormones in most birth control methods. When that happens, your body clears the hormones before they can do their job.

The big offenders include:

• Carbamazepine (Tegretol)
• Oxcarbazepine (Trileptal)
• Phenytoin (Dilantin)
• Phenobarbital
• Primidone (Mysoline)
• Topiramate (Topamax) - especially at doses over 200 mg/day
• Felbamate (Felbatol)

Studies show these drugs can drop estrogen levels by up to 60% and progestin by half. That’s not a small drop - it’s enough to make birth control pills useless. Even if you take them at the same time every day, your body is flushing the hormones out too fast.

What Birth Control Methods Are Affected?

Any birth control that relies on hormones absorbed through the liver is at risk:

• Combined oral contraceptive pills (COCs)
• The patch (Ortho Evra)
• The vaginal ring (NuvaRing)

These all deliver estrogen and/or progestin that get broken down by the same liver enzymes the anticonvulsants activate. The result? Less hormone in your bloodstream. Less protection.

Emergency contraception is also compromised. Levonorgestrel (Plan B, Next Choice) loses about half its effectiveness. Ulipristal acetate (Ella) may not work at all if you’re on enzyme-inducing drugs. That means if you need emergency birth control after unprotected sex, standard options might fail.

What Birth Control Still Works?

Good news: not all methods are affected. Some work just fine - even with strong anticonvulsants.

• 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. It works by creating a local reaction in the uterus. Anticonvulsants don’t touch it. It’s 99% effective and lasts up to 12 years.
• Depo-Provera (DMPA): This shot delivers a very high dose of progestin every 12-13 weeks. Even with faster metabolism, the levels stay high enough to prevent ovulation.
• Progestin-only pills (mini-pills): These are tricky. While they don’t contain estrogen, some studies suggest enzyme inducers might still lower their effectiveness. They’re not the best choice unless combined with another method.

Experts from ACOG and the CDC agree: IUDs and the shot are the safest bets for women on enzyme-inducing anticonvulsants.

The Lamotrigine Problem: A Two-Way Street

Lamotrigine (Lamictal) is different. It doesn’t boost liver enzymes - but it’s still dangerous to mix with estrogen-containing birth control.

Here’s the twist: birth control pills lower lamotrigine levels by about 50%. That means your seizure control could suddenly worsen. Many women don’t realize their seizures are getting worse because they think it’s stress or sleep loss. But it’s the pill.

And when you stop taking the pill - during your week off - lamotrigine levels spike. That can cause dizziness, blurred vision, or even dangerous skin rashes. This cycle of low and high levels is risky.

Doctors recommend avoiding estrogen-containing birth control if you’re on lamotrigine. If you must use it, your lamotrigine dose may need to be increased by 50-100%, and levels must be monitored closely. Non-hormonal options like the copper IUD are often the best solution.

What About Safer Anticonvulsants?

If you’re planning to start birth control - or already on it - ask your neurologist if switching to a safer anticonvulsant is possible. Some newer drugs don’t interfere with hormones:

• Valproate (Depakote) - doesn’t affect birth control, but has other risks in pregnancy
• Gabapentin (Neurontin)
• Pregabalin (Lyrica)
• Levetiracetam (Keppra)
• Perampanel (Fycompa)
• Brivaracetam (Briviact)

These drugs don’t trigger liver enzymes the same way. That means your birth control stays effective, and your seizure control stays stable. Switching isn’t always easy - especially if you’ve had seizures for years - but it’s worth discussing.

Real Stories: What Happens When No One Warns You

A 2019 study of 327 women with epilepsy found that 42% had breakthrough bleeding while on birth control pills and enzyme-inducing drugs. Almost 1 in 5 had an unplanned pregnancy - even though they took their pills correctly.

One Reddit user wrote: “I got pregnant on Ortho Tri-Cyclen while taking Tegretol. My neurologist never said a word.”

Another shared: “After switching from pills to Mirena when I started Keppra, my periods became regular and my seizures didn’t change. Finally, peace of mind.”

These aren’t outliers. They’re common. And the biggest problem? Most women aren’t warned.

A 2022 survey by the Epilepsy Foundation found only 35% of women with epilepsy received contraceptive counseling from their neurologist. Only 22% got it from their gynecologist. That’s a massive gap in care.

What Should You Do?

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

1. Check your drug. Is it one of the enzyme-inducing ones? If yes, your birth control is likely compromised.
2. Don’t panic. But do act. Talk to both your neurologist and your gynecologist - together, if possible.
3. Switch to an IUD or shot. These are the most reliable options. The copper IUD is hormone-free and lasts 12 years. Mirena or Kyleena are progestin-only and just as effective.
4. If you must use pills, use the highest dose available (at least 50 mcg ethinyl estradiol) and always use condoms as backup. Even then, effectiveness is still reduced.
5. Never rely on Plan B if you’re on enzyme-inducing drugs. It probably won’t work.

Why This Matters Beyond Pregnancy

Unplanned pregnancy isn’t just inconvenient - it’s dangerous for women on anticonvulsants. Many of these drugs increase the risk of birth defects by 30-40%. The baseline risk for birth defects in the general population is 2-3%. For women on carbamazepine or phenytoin, it’s 6-10%.

That’s why preventing unintended pregnancy isn’t just about avoiding a baby - it’s about protecting a future baby from serious harm.

Also, if you’re on lamotrigine and get pregnant unexpectedly, your seizure risk could rise - and so could the risk of dangerous side effects from sudden lamotrigine level changes.

What’s Changing in 2026?

There’s new hope. The NIH is tracking 5,000 pregnancies to better understand how different anticonvulsants affect birth outcomes. The Bill & Melinda Gates Foundation is funding research into a non-hormonal contraceptive gel that works without touching liver enzymes - potentially solving this problem for good.

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

But until then - if you’re on anticonvulsants and birth control - don’t assume it’s working. Ask. Check. Switch if needed. Your body, your future, and your health deserve nothing less.