Supplement analysis backed by scientific evidence · PT

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Moderate evidenceVitamins & minerals

Vitamin B1 (Thiamine)

Thiamine is life-saving in deficiency states — Wernicke's encephalopathy, beriberi, refeeding syndrome — and deficiency is common in alcohol use disorder, after bariatric surgery, and in diuretic-treated heart failure. Outside those settings, supplementing does not improve energy, mood, or performance.

What the science says

  • Treats and prevents Wernicke's encephalopathy Strong evidence

    European Federation of Neurological Societies guidance recommends parenteral thiamine 200 mg three times daily for suspected Wernicke's, given before any glucose load, because untreated cases progress to irreversible Korsakoff syndrome or death. The evidence base is largely clinical and observational, but the effect size in acute deficiency is unambiguous and no ethical placebo trial exists.

  • Modestly improves ejection fraction in heart failure Moderate evidence

    A meta-analysis of randomised trials in heart failure patients found thiamine supplementation improved left ventricular ejection fraction by roughly 3-5 percentage points versus placebo, plausibly because loop diuretics increase urinary thiamine loss. Trials were small and short, and no mortality benefit has been shown, so this stays moderate at best.

  • Boosts energy or reduces fatigue in people with adequate intake Limited evidence

    Thiamine is a coenzyme in carbohydrate metabolism, which drives a lot of 'energy vitamin' marketing, but no controlled trial shows added thiamine improves subjective energy, cognition, or exercise capacity in replete adults. Correcting deficiency helps; topping up a normal level does not.

  • Improves diabetic complications (benfotiamine) Limited evidence

    Benfotiamine, a lipid-soluble thiamine derivative, showed early promise for diabetic neuropathy and microvascular endpoints at 300-600 mg/day, but subsequent trials have been inconsistent and generally failed to show meaningful change in HbA1c or nerve conduction. Treat as unproven.

Dosage & safety

Studied doseRDA is 1.2 mg/day for men and 1.1 mg/day for women. Typical supplement doses are 50-100 mg/day. Heart failure trials used 100-300 mg/day orally for 4-12 weeks. Wernicke's encephalopathy protocols use 200-500 mg IV three times daily for 2-3 days, then oral maintenance. Benfotiamine studies used 300-600 mg/day.
SafetyOral thiamine is extremely well tolerated with no established upper limit — excess is excreted in urine. Rare anaphylaxis has been reported with rapid intravenous administration, so IV dosing belongs in a clinical setting. Give thiamine before or alongside IV glucose in at-risk patients (alcohol use disorder, malnutrition, hyperemesis), since a glucose load in a thiamine-deficient person can precipitate Wernicke's. Loop diuretics, chronic alcohol use, bariatric surgery and prolonged vomiting all increase requirements. No meaningful drug interactions at supplemental doses.

Scientific references

Where to buy

NOW Foods, B-1, 100 mg, 100 Tablets

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