Does vitamin B6 interact with any medications?

Several antiepileptic drugs speed up the breakdown of vitamin B6, lowering blood levels and raising homocysteine.

What this means for you

This page has two halves and they pull in opposite directions, which is exactly why it is worth reading rather than skimming.

Some antiepileptic drugs, including valproic acid, carbamazepine and phenytoin, speed up the breakdown of vitamin B6. People taking them can end up with low blood levels. That is an argument for checking, not for self-dosing.

Not for everyone. The reason not to fix that on your own: taking 1 to 6 grams of oral pyridoxine a day for a year or more causes severe and progressive nerve damage in the arms and legs. The upper limit is 100 mg a day.

Between those two facts sits the practical advice. If you are on one of those drugs, raise B6 with your neurologist rather than buying the 100 mg tablets, because the dose that corrects a deficiency and the dose that causes nerve damage are not as far apart as the shelf implies.

Levodopa for Parkinson's disease

Unsettled. Levodopa uses vitamin B6 up, and it shows in blood tests. Across a small set of observational studies, 60 of 145 patients had an abnormal level and 52 of those were low rather than high. Low B6 turned up in 44.6 per cent of people on the intestinal gel form of levodopa and 30.1 per cent on the oral one, where nearly every case came from doses of 1,000 mg a day or more. The reviewers describe their own source literature as limited and built from small studies, and none of it says what to do about the finding. That part belongs to a neurologist.

The combined contraceptive pill

Unsettled. Combined oral contraceptives lower B6 too. Eight young women taking them completed a crossover trial of 100 mg a day for four weeks, and their depression scores fell 20 per cent while the placebo stretch saw the same women rise 11 per cent. Their mood profile scores did not change at all. Eight people, described as preliminary data by the researchers who ran it, at a dose sitting on the upper limit. Worth raising with a doctor, and not worth copying.

When B6 is the thing bolted onto a drug

The tablets prescribed for early pregnancy sickness pair pyridoxine with doxylamine, an antihistamine. That matters when you read the results, because what has been tested is the pair rather than the vitamin.

Established. In the largest recent trial, 352 women across 13 hospitals, doxylamine with pyridoxine cut the nausea score by one point more than placebo on a scale that runs from 3 to 15. Acupuncture alone managed 0.7 of a point and the two together 1.6. The researchers say themselves that they do not know whether a difference that size means anything to a patient.

Not for everyone. The same trial turned up something nobody went looking for. Babies born small for gestational age were more common in the doxylamine-pyridoxine group, an odds ratio of 3.8 with a confidence interval running from 1.0 to 14.1. A secondary outcome with an interval that wide is a reason to watch rather than a demonstrated harm, and it belongs to the combination. If you have that prescription, raise it with whoever wrote it instead of stopping on your own.

The one place where the form of B6 is the treatment

Almost everywhere else on this site, the form of a vitamin is a marketing detail. There is one exception, and it is worth knowing because it is the honest origin of the claim that P5P is the better B6.

PNPO deficiency is a rare inherited epilepsy that starts in newborns, and the body cannot convert ordinary pyridoxine into the active form. Of 49 patients treated with pyridoxal-5'-phosphate, 38 responded, and their survival improved against untreated siblings with the same condition. Ordinary pyridoxine had already been tried and had failed in 30 of the 33 responders, which is nine in ten. Here the word on the label decides whether a child keeps seizing.

Not for everyone. That treatment carries a cost, and it is the reason high-dose P5P off a shelf is a bad idea. Among those same 49 patients, 10 had raised liver enzymes, nine of them after more than a year on it, and two developed cirrhosis confirmed by biopsy. Both of those needed 50 to 100 mg for every kilogram of body weight per day to control seizures, which in an adult would be grams. One more was poisoned at 74 mg per kilogram because a food supplement label was unclear about its contents. None of that applies to a 10 mg B-complex. All of it applies to the idea that the active form is automatically the gentler one.

Unsettled. One more thing about the 100 mg upper limit named above. It is the American figure, and EFSA cut its European equivalent to 12 mg a day in 2023, eight times lower. The Netherlands capped supplements at 21 mg a day in 2018. If you are taking B6 alongside a drug that lowers it, that gap is the reason to settle the dose with the person treating you rather than with a shelf. The dose that corrects a deficiency and the dose one regulator already considers unsafe overlap.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Full guide: Vitamin B6: a water-soluble vitamin that can still damage nerves permanently