Quick answer

Ask your pharmacist or doctor before combining. Official sources document four supplements for anti-seizure medicines: folate, vitamin B6, biotin and B complex. NIH and drug labels show the interaction running both ways, with the medicines lowering vitamin levels and folic acid lowering phenytoin levels, and MedlinePlus warns against stopping a seizure medicine suddenly.^1,2,3

Key facts

NIH says valproic acid, carbamazepine and phenytoin speed up the breakdown of vitamin B6 and can lower its blood levels.⁴
The phenytoin and folic acid labels both say folic acid can lower phenytoin levels or weaken its effect.^2,5
In a study of 264 people with epilepsy, a year or more on anticonvulsants was linked to lower biotin levels.⁶
MedlinePlus warns that stopping phenytoin suddenly may make seizures worse.³
MedlinePlus also names St. John's wort, vitamin D and antacids with calcium, magnesium or aluminum for phenytoin.³

What are anti-seizure medicines, and why do vitamins come up?

Anti-seizure medicines, also called anticonvulsants, are taken to control seizures. MedlinePlus describes phenytoin as one that works by decreasing abnormal electrical activity in the brain, and carbamazepine as one that does the same and is also prescribed for some facial nerve pain and for manic episodes. Those two pages stand in for the class here, so other medicines in it, such as valproate, phenobarbital and primidone, may differ on their own labels.^3,7

The sources checked show the interaction running in both directions. Some seizure medicines lower the body's supply of a vitamin, and some vitamins may lower the blood level of the medicine. Each entry below says which direction it describes.^4,8

Do not stop or change a seizure medicine because of anything on this page. MedlinePlus warns that stopping phenytoin suddenly may make seizures worse, and says the same about carbamazepine for people with a seizure disorder. Talk to your doctor first.^3,7

Can folic acid lower the level of a seizure medicine?

Folate has the firmest footing of the four, because two drug labels speak to it. The phenytoin label lists folic acid among products that can lower phenytoin blood levels, and the folic acid label says it can weaken phenytoin's effect.^2,5

Ask your pharmacist or doctor first

Phenytoin, carbamazepine and valproate can lower blood folate, and folate supplements might lower blood levels of these medicines. The phenytoin and folic acid labels both say folic acid can lower phenytoin levels or weaken its effect.^1,2,5,8

On the medicine's label

Folic acid is also something NIH advises for anyone who could become pregnant, and NIH lists anti-seizure medicines among the medicines folate interacts with. Both statements sit on the same consumer fact sheet. That is a conversation for your prescriber, not a decision to make alone.¹

Does vitamin B6 change seizure medicine levels?

Ask your pharmacist or doctor first

Valproic acid, carbamazepine and phenytoin speed up the breakdown of vitamin B6 and can lower its blood levels, which NIH says could reduce the drugs' ability to control seizures. Research also suggests that 200 mg a day of pyridoxine can lower blood levels of phenytoin and phenobarbital; whether smaller amounts do this is not known.^4,9

Reported in studies

The research in that entry used 200 mg a day of pyridoxine, a form of B6. NIH lists a US upper limit of 100 mg a day for adults, so that amount was twice the upper limit, and the entry says it is not known whether smaller amounts have the same effect.^4,9

Do seizure medicines lower biotin?

Your doctor may want to check on you

In a study of 264 people with epilepsy, taking anticonvulsants such as carbamazepine, phenytoin, phenobarbital or primidone for a year or more was linked to lower biotin levels. These medicines may speed up the breakdown of biotin and reduce its absorption.^6,10

Reported in studies

This entry describes the medicine lowering biotin, not biotin changing the medicine. NIH adds that biotin above the recommended intake can make some lab tests read falsely high or low, so mention any biotin supplement before blood work.^6,10

What about a B complex with a seizure medicine?

A B complex product can combine several B vitamins, so its entry repeats the concerns from the folate, vitamin B6 and biotin entries in one place.^11,12,13

Ask your pharmacist or doctor first

Anticonvulsants such as phenytoin, carbamazepine and valproate can lower folate and vitamin B6 levels, and long-term use has been linked to lower biotin. Folate supplements might lower blood levels of these medicines, and 200 mg a day of vitamin B6 lowered blood levels of phenytoin and phenobarbital.^11,12,13

Reported in studies

Read the Supplement Facts panel for folic acid, vitamin B6 (pyridoxine) and biotin, and bring the bottle to your appointment.

Do St. John's wort, vitamin D or antacids matter with seizure medicines?

The four entries above are the ones documented for this class. MedlinePlus names more for the two medicines it covers: St. John's wort, antacids that contain calcium, magnesium or aluminum, vitamin D and folic acid for phenytoin, and St. John's wort for carbamazepine. NCCIH also lists anticonvulsants among the kinds of medicine ashwagandha might interact with.^3,7,14

Those mentions come without the detail of a drug label, so treat them as questions to ask, not as findings about every seizure medicine.

What do the severity labels and 'reported in studies' notes mean here?

The four anti-seizure entries, by direction, how they are known and the label shown^2,4,6
Supplement	What is described	How it is known	Label shown
Folate	Folic acid may lower phenytoin levels, and the medicines can lower folate	On the medicine's label	Ask your pharmacist or doctor first
Vitamin B6	The medicines can lower B6, and 200 mg a day of B6 lowered two medicines' levels	Reported in studies	Ask your pharmacist or doctor first
B complex	The folate and B6 concerns, plus biotin	Reported in studies	Ask your pharmacist or doctor first
Biotin	Long use of the medicines is linked to lower biotin	Reported in studies	Your doctor may want to check on you

One entry rests on a drug label and three on studies, and none is the merely expected kind. Biotin carries the monitor label, which means a doctor may want to check on you, not that anything should be avoided.

What to ask your pharmacist or the doctor who prescribes your seizure medicine

Which anti-seizure medicine am I taking, and does its label mention folic acid, vitamin B6 or biotin?
Is any vitamin or herbal product I use on the list for my medicine, including St. John's wort?³
Should the blood level of my medicine be checked if I start or stop a vitamin?
Folic acid is advised for pregnancy. How should it fit with my medicine?¹

Questions people ask

Which supplements interact with anti-seizure medicines?

Official sources document four: folate, vitamin B6, biotin and B complex. NIH and drug labels describe the medicines lowering some vitamin levels, and folic acid or high-dose B6 possibly lowering medicine levels. MedlinePlus also names St. John's wort, vitamin D and some antacids for phenytoin.^1,3,4

Which vitamins should you not take with anti-seizure medicines?

The vitamins in the sources checked are folic acid, vitamin B6 and biotin, plus B complex products that can contain them. None is simply labeled avoid, so ask your pharmacist before starting or stopping any of them.^4,6,8

What supplements should you avoid with anti-seizure medicines?

The sources checked list specific effects, not a set of supplements to avoid: folic acid lowering phenytoin levels, and 200 mg a day of vitamin B6 lowering phenytoin and phenobarbital levels. Ask your pharmacist about any supplement, and do not stop a seizure medicine on your own.^2,3,4

Do anti-seizure medicines lower vitamin levels?

NIH says valproic acid, carbamazepine and phenytoin can lower vitamin B6 and folate, and a study of 264 people with epilepsy linked a year or more of anticonvulsants to lower biotin. Ask your doctor whether your levels should be checked.^4,6,8

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This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.