When you’re pregnant, taking folic acid isn’t just a suggestion-it’s one of the most important things you can do for your baby’s development. But here’s the part most people don’t talk about: folic acid doesn’t play nice with every medication. If you’re on seizure drugs, antibiotics, or even acid reflux pills, your folic acid might not work the way it should-and that could put your baby at risk.
Why Folic Acid Matters So Much in Pregnancy
Folic acid is the synthetic form of vitamin B9, and it’s the reason neural tube defects like spina bifida and anencephaly have dropped by nearly half since 1998. That’s when the U.S. started requiring it in flour, bread, and cereals. But even with fortified foods, most women still need a supplement. The CDC recommends 400 micrograms (mcg) daily before conception and 600 mcg during pregnancy. Why? Because the neural tube-the structure that becomes your baby’s brain and spinal cord-closes by day 28 after conception. Most women don’t even know they’re pregnant that early.
Prenatal vitamins usually contain between 600 and 1,000 mcg of folic acid. Some prescription versions go even higher, especially for women with epilepsy or a history of a previous neural tube defect. But more isn’t always better. The upper limit for adults is 1,000 mcg per day. Going over that doesn’t give you extra protection-it might just pile up in your system as unmetabolized folic acid, which some researchers are still studying for long-term effects.
Medications That Fight Folic Acid
Not all drugs are harmless when paired with folic acid. Some actually fight it-reducing its effectiveness or making your medication less powerful. Here are the big ones:
- Anticonvulsants like phenytoin (Dilantin), carbamazepine (Tegretol), and valproic acid (Depakote) are known to lower folic acid levels. In fact, women on these drugs have a 1 in 20 chance of having a baby with a neural tube defect-five times higher than average. That’s why neurologists often recommend 4,000 to 5,000 mcg daily during pregnancy. But here’s the twist: high-dose folic acid can also reduce how well these seizure meds work. One Reddit user, u/AnxiousMom2022, reported breakthrough seizures after starting a standard prenatal vitamin. Her doctor later realized the folic acid was interfering with her phenytoin levels.
- Methotrexate, used for autoimmune diseases and sometimes ectopic pregnancies, works by blocking folate. Giving folic acid alongside it can reduce side effects like nausea and liver stress-but only if timed correctly. Doctors often prescribe low-dose folic acid (5-10 mg weekly) to protect healthy cells while letting methotrexate do its job on abnormal ones.
- Sulfasalazine, used for ulcerative colitis and rheumatoid arthritis, blocks folic acid absorption in the gut. The UK’s NICE guidelines say you should never take this drug with folic acid without medical supervision. Your doctor may need to switch you to L-methylfolate, a form your body can use even if absorption is impaired.
- Pyrimethamine, used to treat toxoplasmosis during pregnancy, also interferes with folate metabolism. When you add folic acid, your doctor may need to adjust the dose to keep the infection under control while protecting your baby.
- Antacids and proton pump inhibitors (like omeprazole or Tums) lower stomach acid, which is needed to absorb folic acid. If you take these regularly, you could be losing up to 50% of your folic acid intake. Taking your prenatal vitamin on an empty stomach, at least two hours before or after your acid reflux meds, helps.
Iron and Calcium: The Silent Folic Acid Killers
Iron is a key ingredient in most prenatal vitamins-and it’s essential for preventing anemia. But here’s the catch: iron and folic acid compete for absorption in your gut. A 2017 study in the American Journal of Clinical Nutrition found that taking them together reduces folic acid absorption by 20-30%. That’s why many OB-GYNs now recommend splitting them up: take your prenatal vitamin in the morning with water, and your iron supplement at night with vitamin C-rich food like orange slices or bell peppers.
Calcium has a similar effect. If you take calcium supplements or drink a glass of milk with your prenatal vitamin, you could be cutting folic acid absorption by 25%. The FDA recommends taking folic acid on an empty stomach with water, and waiting at least two hours before eating calcium-rich foods like cheese, yogurt, or fortified plant milks.
What About MTHFR? Your Genetics Matter
One in five people have a gene variant called MTHFR 677C>T. It’s more common in Hispanic populations (up to 25%) and affects how your body converts folic acid into its active form, L-methylfolate. If you have this variant, your body might not use the folic acid in your prenatal vitamin efficiently-no matter how much you take.
For years, doctors told people with MTHFR to switch to L-methylfolate supplements. But the science isn’t clear-cut. The CDC says there’s no proven benefit for the general population, and most women with MTHFR do fine on regular folic acid. Still, if you’ve had a previous pregnancy affected by a neural tube defect, or if you’ve been told you have high homocysteine levels, your doctor might recommend Quatrefolic® or other forms of methylfolate. The first prenatal vitamin with Quatrefolic® got FDA approval in 2023, but it costs nearly $46 a month-far more than standard options.
What to Do If You’re on Medications
If you’re taking any prescription or over-the-counter drugs, don’t assume your prenatal vitamin is safe to take as-is. Here’s what to do:
- Make a list of every medication, supplement, and herb you take-including antacids, antibiotics, and CBD oil.
- Bring it to your OB-GYN and pharmacist. Pharmacists at CVS and Walgreens now offer free medication reviews for pregnant patients. Ask: “Could any of these interfere with my folic acid?”
- Ask about timing. Can you take your iron at night? Can you split your folic acid into two doses? Can you switch from an antacid to a different heartburn remedy?
- Don’t stop or change anything without talking to your doctor. Stopping seizure meds or methotrexate on your own is far riskier than any interaction with folic acid.
What About Side Effects?
Most women tolerate folic acid just fine. But if you’re getting sick to your stomach with your prenatal vitamin, it’s probably not the folic acid-it’s the iron. A 2023 survey of over 2,000 pregnant women found that 78% had nausea from iron-containing prenatal vitamins. Many switched to taking folic acid alone (400-800 mcg) and iron separately. That cut nausea in half for most.
Some people report headaches or trouble sleeping with high-dose folic acid, but those are rare. The bigger risk? Not taking enough. The CDC says 400 mcg daily reduces neural tube defect risk by 50-70%. Skipping it-even for a few weeks-can have lasting consequences.
What’s New in 2025?
The CDC is pushing to fortify corn masa flour with folic acid by 2025. Why? Hispanic women have 20-30% higher rates of neural tube defects, and corn tortillas are a staple in many diets. Right now, most fortified foods are wheat-based, so this change could help thousands.
Researchers are also looking into whether folic acid reduces autism risk. A 2022 study of 45,000 children found a 40% lower risk with periconceptional folic acid. But a 2021 Danish study found no link. The science is still evolving. For now, the recommendation stays the same: start at 400 mcg before you get pregnant, and keep going through the first trimester.
Bottom Line
Folic acid is powerful-but it’s not magic. It works best when it’s not fighting other drugs, when it’s taken correctly, and when your body can actually use it. If you’re on any medication, don’t just swallow your prenatal vitamin and hope for the best. Talk to your doctor. Ask your pharmacist. Time your doses. Know your genetics. These small steps can make the difference between a healthy pregnancy and a preventable complication.
Can I take folic acid with my prenatal vitamin if I’m on seizure medication?
Yes-but only under strict medical supervision. Women on anticonvulsants like carbamazepine or phenytoin need much higher doses of folic acid-up to 5,000 mcg daily-to prevent neural tube defects. But high-dose folic acid can reduce the effectiveness of these drugs. Your neurologist and OB-GYN must work together to balance seizure control with fetal protection. Never adjust your dose on your own.
Does iron in prenatal vitamins block folic acid absorption?
Yes. Taking iron and folic acid together reduces folic acid absorption by 20-30%. To fix this, take your prenatal vitamin in the morning on an empty stomach, and take your iron supplement at night with vitamin C. Some women choose to split them into two separate pills to avoid nausea and improve absorption.
Should I switch to L-methylfolate if I have MTHFR?
Not necessarily. Most women with MTHFR variants do fine on standard folic acid. The CDC doesn’t recommend routine switching because there’s no strong evidence it improves outcomes for the average pregnancy. But if you’ve had a previous neural tube defect, high homocysteine levels, or your doctor suspects poor absorption, L-methylfolate (like Quatrefolic®) may be worth considering. It’s more expensive, but it bypasses the genetic bottleneck.
Can antacids like Tums reduce folic acid absorption?
Yes. Antacids and proton pump inhibitors lower stomach acid, which your body needs to break down and absorb folic acid. Studies show this can cut absorption by up to 50%. Take your prenatal vitamin at least two hours before or after any acid-reducing medication. If you rely on antacids daily, talk to your doctor about safer alternatives for heartburn.
Is it safe to take more than 1,000 mcg of folic acid during pregnancy?
Only under medical direction. The upper limit is 1,000 mcg per day for adults. While no major health risks have been confirmed, taking more than that without a clear medical reason can lead to unmetabolized folic acid building up in your blood. This is especially true if you’re taking high-dose supplements on top of fortified foods. Stick to your doctor’s recommendation-don’t double up on prenatal vitamins or add extra folic acid without guidance.
Next Steps
If you’re planning to get pregnant-or already are-here’s what to do right now:
- Check your prenatal vitamin label. Does it have at least 600 mcg of folic acid?
- Write down every medication, supplement, and OTC drug you take.
- Call your pharmacist and ask: “Which of these might interfere with folic acid?”
- If you’re on seizure meds, sulfasalazine, or methotrexate, schedule a consult with your OB-GYN and specialist.
- If you’re unsure about MTHFR, ask your doctor for a simple blood test for homocysteine levels. It’s cheap and fast.
Folic acid is one of the few things in pregnancy where a simple, cheap, daily habit can prevent lifelong disabilities. But it’s not a one-size-fits-all solution. Your body, your meds, your genetics-they all matter. Don’t skip the conversation. It could change everything.
Jessica Salgado
December 16, 2025 AT 16:34I had no idea folic acid could mess with my seizure meds until I started having breakthrough seizures after switching to a standard prenatal. My neurologist nearly had a heart attack when he saw my phenytoin levels. Turns out, that 800 mcg in my CVS prenatal was literally fighting my medication. Now I’m on 5,000 mcg of methylfolate and my seizures are under control. Don’t assume your OB knows what your neurologist needs-get them talking.
Linda Caldwell
December 17, 2025 AT 18:42Just started trying to conceive and this post saved me from a disaster. I was taking Tums with every meal and my prenatal at breakfast. Now I take my vitamin on an empty stomach and save the antacids for after dinner. So simple. So life-changing. Thank you for the real talk.
Anna Giakoumakatou
December 18, 2025 AT 22:33Oh wow. A post that doesn’t just say ‘take your vitamins’ like a wellness influencer on a sponsored tour. Who knew medicine had actual science behind it? Shocking. I’m crying. Not really. But I’m definitely not taking your prenatal unless you’ve had a genetic panel and a pharmacist on speed dial.
CAROL MUTISO
December 19, 2025 AT 16:01Let’s be real-folic acid isn’t magic, it’s a biochemical handshake between your genes, your meds, and your gut. And most doctors treat it like a checkbox. I’m a pharmacist. I’ve seen women on methotrexate take 1,000 mcg and wonder why their joints are screaming. The body doesn’t care about ‘recommended doses’-it cares about bioavailability. L-methylfolate isn’t a luxury, it’s a workaround for a broken system. And yes, it’s expensive. But so is a child with spina bifida. We need to stop pretending nutrition is one-size-fits-all. It’s not. It’s biology. And biology is messy.
Erik J
December 21, 2025 AT 13:58Interesting. I’ve been on sulfasalazine for 8 years and just started trying for a baby. My OB said ‘just take the prenatal.’ I didn’t know it blocked absorption. I’ll ask my GI doc about switching to methylfolate. Thanks for the heads-up.
BETH VON KAUFFMANN
December 22, 2025 AT 11:58Let’s cut through the noise: 400 mcg is enough for 95% of people. The rest? They’re either on meds that interfere or have MTHFR. But the fearmongering around ‘unmetabolized folic acid’ is overblown. The FDA didn’t set a 1,000 mcg cap because it’s dangerous-it’s because they’re scared of lawsuits. You want to take 5,000 mcg? Fine. Just don’t pretend it’s ‘better.’ It’s just more. And yes, your prenatal vitamin probably has too much iron. That’s why you’re puking. Not the folic acid.
Martin Spedding
December 24, 2025 AT 00:12so u said take prenatal on empty stomach but then u say take iron at night with orange? that’s like saying ‘don’t eat carbs with protein’ but then u eat steak and rice. logic? nah. also TUMS ARE FINE. my mom took them for 3 pregnancies. baby fine. stop scaring ppl.
Raven C
December 24, 2025 AT 09:28While I appreciate the earnestness of this post, I must express my profound concern regarding the casual dismissal of unmetabolized folic acid’s potential epigenetic implications. The literature, though still nascent, suggests a disturbing correlation between prolonged exposure and altered DNA methylation patterns in offspring. One must ask: are we optimizing for neural tube closure-or inadvertently programming neurodevelopmental vulnerability? This isn’t ‘just a vitamin.’ It’s a pharmacological intervention with systemic consequences. I urge you to consult the 2024 Lancet meta-analysis before proceeding.
Donna Packard
December 25, 2025 AT 09:10This is so helpful. I was so scared to take anything because I didn’t know what was safe. Now I feel like I can actually plan instead of panic. Thank you for making this so clear.
Patrick A. Ck. Trip
December 25, 2025 AT 12:23Thank you for this comprehensive and deeply thoughtful analysis. I am currently on methotrexate for psoriatic arthritis and was unaware of the interaction with folic acid. I will schedule a consultation with my rheumatologist and OB-GYN immediately to coordinate timing and dosage. Your guidance has provided clarity during a time of immense uncertainty.
Sam Clark
December 26, 2025 AT 18:32As a clinical pharmacist specializing in maternal health, I’ve seen too many patients assume ‘prenatal = safe.’ This post nails the nuance. The real issue isn’t folic acid-it’s the lack of coordinated care. OBs, neurologists, GI specialists, and pharmacists rarely talk. If you’re on any chronic med, insist on a med review. It’s your right. And yes, split your iron. Your gut will thank you.
Salome Perez
December 26, 2025 AT 19:26As a Latina mom of three, I’m thrilled the CDC is fortifying corn masa. My abuela always ate tortillas daily-and we never had prenatal vitamins. Now I know why my sister’s baby had a neural tube defect. This isn’t just science-it’s equity. If we want to close the gap, we need to meet people where they eat. Thank you for including this.
Kent Peterson
December 28, 2025 AT 12:53Wow. A whole article about folic acid. Did you forget we have a $200K baby healthcare crisis? We’re spending millions on supplements while families can’t afford diapers. This isn’t ‘empowerment’-it’s medical capitalism dressed up as advice. Take your 400 mcg. Stop overcomplicating. And if your baby has a defect? Blame the system-not your vitamin.