Vitamin B1 (Thiamine)

thiamine · thiamin · benfotiamine · vitamin B1 · thiamine hydrochloride

Snapshot

Indications	Contraindications
Thiamine deficiency¹ Wernicke-Korsakoff syndrome² Beriberi¹ Post-bariatric deficiency³ Hyperemesis gravidarum⁴ Heart failure with diuretics⁵ Diabetic neuropathy¹	Pregnancy or nursing, per some labels⁶ Known soy allergy, some products⁶

Thiamine (vitamin B1) is a water-soluble vitamin that acts as a cofactor in glucose, amino acid, and lipid metabolism¹. Supplementation targets deficiency, which impairs cellular energy production and causes neurologic and cardiac disease⁷. Chronic alcohol use appears to be the most common cause in industrialized countries¹. Bariatric surgery and heart failure treated with long-term furosemide are other typical settings. Thiamine markers also run lower in diabetes⁸.

The Cochrane review of alcohol-related Wernicke-Korsakoff syndrome found randomized evidence insufficient to set dose, route, or duration². In heart failure, a 2023 meta-analysis of randomized trials found no effect on most outcomes⁹. A 2022 systematic review found that irritable bowel syndrome exclusion diets were associated with lower vitamin B1 intake, and it noted a lack of interventional micronutrient studies¹⁰. Products supply thiamine mononitrate or hydrochloride, or the synthetic derivative benfotiamine; see Form comparison¹.

Thiamine is not known to interact with medications, but furosemide and fluorouracil can lower thiamine status¹. Per the National Institutes of Health fact sheet, people taking such medications regularly are advised to discuss thiamine status with their health care providers¹.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

92 sources, 76 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources