Vitamin B6Vitamin

• Nausea and vomiting in pregnancyLikely helps

  ACOG recommends 10–25 mg of B6, three to four times daily, as first-line therapy for nausea and vomiting of pregnancy [1].
  
  Two RCTs found 30–75 mg/day of pyridoxine significantly reduced nausea [1].
  
  B6 combined with the antihistamine doxylamine cut nausea and vomiting by about 70%, with lower hospitalisation rates [1]. ^[1]

• Premenstrual syndromePossibly helps

  A meta-analysis of 9 trials in roughly 1,000 women found B6 outperformed placebo on PMS symptoms [1].
  
  Its own authors flagged the pooled result as limited by poor methodological quality in most of those trials [1].
  
  A more recent RCT using 80 mg/day of pyridoxine across three cycles reported a significant reduction across a broad range of PMS symptoms [1]. ^[1]

• Carpal tunnel syndromePossibly helps

  A popular self-remedy on genuinely contested evidence. A review of 14 studies found none of them provided top-tier level-I evidence either way [2].
  
  Some small studies linked B6 deficiency to carpal tunnel syndrome and reported improvement on supplementation [2].
  
  Others found nothing at all. 200 mg/day for 12 weeks gave no relief of the symptoms patients rate as most bothersome — pain, numbness and night tingling [2]. ^[2]

• Cognition and moodPossibly helps

  A systematic review of 14 RCTs and a separate Cochrane review both concluded there is insufficient evidence that B6 supplementation improves cognition or mood [1].
  
  That is a gap in the trial record rather than a demonstration that nothing happens [1]. ^[1]

• Cardiovascular eventsNot shown to help

  B6 lowers homocysteine reliably. The Norwegian Vitamin Trial, the Western Norway B Vitamin Intervention Trial and a 5,442-woman RCT all found no reduction in cardiovascular events [1].
  
  Lowering homocysteine simply does not translate into fewer events, per NIH's Office of Dietary Supplements [1].
  
  One result cuts the other way. HOPE-2 gave 50 mg/day B6 with 1 mg B12 and 2.5 mg folic acid for 5 years and saw a 25% relative stroke risk reduction [1].
  
  HOPE-2 had no B6-only arm, so that stroke result cannot be assigned to B6 specifically [1]. ^[1]

• Cancer riskNot shown to help

  Observational data and trial data split cleanly here.
  
  A meta-analysis of prospective studies found the highest quintile of B6 intake carried 20% lower colorectal cancer risk than the lowest [1].
  
  Supplementation trials found no effect on cancer incidence or mortality [1]. Eating more B6-rich food and swallowing a B6 tablet are not the same intervention. ^[1]

• Isolated B6 deficiency is uncommon — low B6 status usually travels alongside low B12 and folate
• Microcytic anemia
• EEG abnormalities
• Dermatitis with cheilosis — cracked corners of the mouth
• Glossitis — a swollen tongue
• Depression and confusion
• Weakened immune function
• A scaly, red, greasy rash
• Pins-and-needles numbness in the hands and feet
• In infants: irritability, abnormally acute hearing, and convulsive seizures^[1]

• Pyridoxine hydrochloride (HCl)Nearly every clinical study reporting a benefit used pyridoxine, which is why PeaceHealth's health library calls it the…

  Elemental content

  The most common B6 vitamer in supplements — a precursor, not the active coenzyme [1]

  Absorption

  NIH's Office of Dietary Supplements states absorption from supplements resembles absorption from food, without substantial differences between forms [1].
  
  EFSA's 2008 opinion goes further, putting pyridoxine's bioavailability at or above PLP's [4].

  Best for

  Nearly every clinical study reporting a benefit used pyridoxine, which is why PeaceHealth's health library calls it the practical default [6].

• Pyridoxal-5'-phosphate (P5P or PLP)PeaceHealth flags specific exceptions where PLP may work better — B6-responsive anemia, B6-dependent epilepsy, infantil…

  Elemental content

  The body's active coenzyme form, sold directly rather than as a precursor [1]

  Absorption

  Four sources disagree here, and this page leaves the disagreement standing.
  
  NIH ODS finds no substantial difference between forms [1]. EFSA's 2008 opinion puts PLP's bioavailability lower than, or at best equal to, pyridoxine's [4].
  
  ConsumerLab reports similar bioavailability at recommended doses, and no human-study support for PLP's marketed advantages such as diabetes benefit [5].

  Best for

  PeaceHealth flags specific exceptions where PLP may work better — B6-responsive anemia, B6-dependent epilepsy, infantile spasms, autism and carpal tunnel syndrome [6].

• Why the form may matter for safetyNothing yet. This is cell-culture work proposing a mechanism, not a human trial comparing the two forms for safety .

  Elemental content

  A 2017 cell-culture finding specific to pyridoxine, not to PLP or the other vitamers [7]

  Absorption

  Pyridoxine caused dose-dependent cell death and inhibited PLP-dependent enzymes in that model [7].
  
  The authors proposed that high-dose pyridoxine competitively displaces the body's active PLP — the so-called vitamin B6 paradox [7].

  Best for

  Nothing yet. This is cell-culture work proposing a mechanism, not a human trial comparing the two forms for safety [7].

• Sensory neuropathy from long-term high doses

  This is why B6 carries a real upper limit when most water-soluble vitamins carry none.
  
  Chronic oral pyridoxine at 1–6 g/day for 12–40 months has caused severe, progressive sensory neuropathy with ataxia [1]. It usually resolves once the supplement stops.
  
  Some case reports place the onset below 500 mg/day, still five times the US upper limit [2]. ^[1]

• Drugs and conditions that deplete B6

  Antiseizure drugs, the antibiotic isoniazid, hydralazine, corticosteroids and penicillamine all deplete the vitamin [1].
  
  Higher-risk groups include people with impaired kidney function, dialysis and transplant patients among them [1].
  
  Also rheumatoid arthritis, celiac disease, Crohn's disease, ulcerative colitis, and alcohol dependence [1]. Severe protein-energy malnutrition and heavily processed diets do the same [1]. ^[1]

• Levodopa taken without carbidopa

  A classic metabolic-interaction study found pyridoxine cut plasma levodopa by 67%, apparently by speeding its breakdown outside the brain [10].
  
  Nearly all modern formulations pair levodopa with carbidopa, a decarboxylase inhibitor, which stops that loss of drug effect [10].
  
  So this mainly matters for anyone on levodopa monotherapy [10]. ^[10]

• Antiepileptic drugs

  Valproic acid, carbamazepine and phenytoin speed up B6 catabolism, lowering active PLP and raising homocysteine [1].
  
  With long-term use that may raise seizure and vascular-event risk [1].
  
  The traffic runs both ways. 200 mg/day of pyridoxine for 12–120 days lowered serum phenytoin and phenobarbital concentrations [1].
  
  WebMD's monograph warns against large B6 doses alongside phenytoin, since reducing the drug's effect raises seizure risk [11]. ^[1]

• Levetiracetam behavioural side effects

  Preliminary evidence suggests B6 may reduce the irritability, agitation and depression associated with the antiepileptic levetiracetam [1].
  
  Doses studied were 50–350 mg/day in children and 50–100 mg/day in adults. Read that as preliminary, not established [1]. ^[1]

• Cycloserine

  The TB antibiotic cycloserine increases urinary loss of pyridoxine, which may worsen the seizures and neurotoxicity associated with the drug [1].
  
  Supplementation is used to offset that loss [1]. ^[1]

• Hydralazine

  The blood-pressure drug hydralazine binds pyridoxal and increases its urinary excretion, which can produce B6 deficiency over time [13].
  
  Some clinicians recommend B6 supplementation for people on long-term hydralazine [13]. ^[13]

• Blood-pressure medication generally

  WebMD's monograph flags a moderate interaction: high-dose B6 may itself lower blood pressure [11].
  
  Alongside antihypertensive drugs that could push blood pressure too low, so the monograph advises monitoring closely [11]. ^[11]

• Amiodarone

  WebMD's monograph flags that B6 taken with amiodarone may increase sun-sensitivity risk [11]. ^[11]

• Theophylline

  People taking theophylline for asthma or COPD often show low PLP [1].
  
  That may contribute to the drug's neurological and central-nervous-system side effects, seizures included [1]. ^[1]

The richest sources are fish, beef liver and other organ meats, starchy vegetables such as potatoes, and non-citrus fruit [1].

About 75% of the B6 in a mixed diet is bioavailable [1].

Per serving: canned chickpeas, 1 cup — 1.1 mg (65% DV). Pan-fried beef liver and cooked yellowfin tuna, 3 oz each — 0.9 mg (53% DV) [1].

Cooked sockeye salmon, 3 oz — 0.6 mg (35% DV). Roasted chicken breast, 3 oz — 0.5 mg (29% DV) [1].

Around 0.4 mg (25% DV) each: fortified breakfast cereal, boiled potatoes, roasted turkey, and a medium banana [1].

Extensive industrial processing, grain refining in particular, strips out much of a food's natural B6 [1].

Morning is the usual suggestion for B vitamins, on the reasoning that they sit in energy metabolism [8].

For B6 there is a sleep-specific reason. A randomised, double-blind, placebo-controlled trial in 100 people gave 240 mg of pyridoxine HCl before bed for five nights [3].

It significantly increased how much dream content participants recalled [3].

Dream vividness, bizarreness and colour did not change significantly. Neither did time awake at night, sleep quality or morning tiredness [3].

On food: B6 is water-soluble and can be taken with or without a meal [9].