Vitamin
Thiamine
Prepared by the ezGLP team. Sources last checked . Profile reviewed .
Also known as Vitamin B1, Thiamine hydrochloride
Routes represented in the knowledgebase: Oral / Subcutaneous (SubQ).
Educational overview
Oral supplement and FDA-approved prescription injection for deficiency; rare serious hypersensitivity can occur with parenteral use.
Thiamine (vitamin B1) is a water-soluble vitamin that cells phosphorylate to thiamine pyrophosphate, the coenzyme for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase, the enzymes that let glucose enter oxidative metabolism and the pentose phosphate pathway. Body stores are small and turn over within weeks, so intake interruptions, persistent vomiting, alcohol dependence, bariatric surgery, diuretic therapy, and refeeding after starvation can deplete it quickly. Deficiency presents as beriberi, with cardiac or neuropathic forms, or as Wernicke's encephalopathy. Supplements contain thiamine hydrochloride or mononitrate; benfotiamine is a lipid-soluble derivative sold as a supplement. A prescription injection of thiamine hydrochloride is used when oral replacement is impossible or too slow.
The requirement for thiamine and the biochemistry of deficiency are settled science, summarised in the NIH Office of Dietary Supplements fact sheet. Clinical evidence for how to treat established deficiency is thinner than expected: a Cochrane review found only limited randomized data on thiamine for preventing or treating Wernicke-Korsakoff syndrome in people with alcohol dependence, so hospital practice rests on physiology, case series, and consensus. Trials of thiamine and benfotiamine for diabetic complications, heart failure, and cognitive decline are small and inconsistent. Case reports of Wernicke's encephalopathy after prolonged vomiting, including in bariatric-surgery populations, underpin the clinical habit of checking or replacing thiamine before glucose is given to anyone at nutritional risk.
In the United States, oral thiamine is a dietary supplement, while Thiamine Hydrochloride Injection USP is an FDA-approved prescription drug marketed under abbreviated new drug applications. Its labelled indications are beriberi, Wernicke's encephalopathy, thiamine deficiency with cardiovascular involvement, and coverage during intravenous dextrose in people with marginal thiamine status when oral therapy is not feasible. The label carries a warning that serious hypersensitivity and anaphylactic reactions, including deaths, have followed intravenous or intramuscular administration, describes an intradermal test dose where sensitivity is suspected, and warns about aluminum accumulation with prolonged parenteral use in impaired kidney function. Thiamine also appears in approved intravenous multivitamin products and in compounded B-complex injections, which are not FDA-approved.
The approved injection is stored at controlled room temperature, protected from light, and used only if the solution is clear with the seal intact. Oral products are stable in a closed container away from heat and moisture, though thiamine degrades in alkaline or heated liquids. For a record, the details that matter are the salt and strength, the route, the lot number, and, for compounded blends, the pharmacy and beyond-use date. Because deficiency develops during periods of poor intake or vomiting, a dose log kept alongside a record of intake problems, weight change, or new neurological symptoms gives a clinician the timeline needed to judge whether thiamine status should be measured or empirically replaced.
- Category
- Vitamin
- Routes represented
- Oral / Subcutaneous (SubQ)
- Storage context
- Follow the product or pharmacy label; requirements vary by route and formulation.
Published literature
No verified PubMed or DOI link is available for this entry.
Common questions
Why is thiamine given by injection?
Because oral absorption is limited and slow when stores are exhausted or the gut is not working. The approved injection is indicated for beriberi, Wernicke's encephalopathy, and deficiency with heart involvement, and for patients receiving intravenous dextrose who may be thiamine-depleted, since glucose metabolism consumes the coenzyme. Parenteral administration reaches the brain and heart within hours, which matters in acute encephalopathy.
Is thiamine injection FDA-approved?
Yes. Thiamine Hydrochloride Injection USP is an FDA-approved prescription product for intramuscular or intravenous use, marketed by several manufacturers under abbreviated new drug applications. It is distinct from compounded B-complex injections, which combine thiamine with other B vitamins and are not approved. The approved label carries an anaphylaxis warning and an aluminum warning specific to prolonged parenteral use in kidney impairment.
What are the warnings on the thiamine injection label?
The label states that serious hypersensitivity and anaphylactic reactions, including deaths, have occurred after intravenous or intramuscular thiamine, particularly with repeated administration, and describes an intradermal test dose where sensitivity is suspected. It warns that the product contains aluminum that may accumulate with prolonged parenteral use when kidney function is impaired. Storage is at controlled room temperature with protection from light.
Can thiamine deficiency happen with prolonged vomiting or rapid weight loss?
Yes. Thiamine stores last only a few weeks, so persistent vomiting, very low intake, and rapid weight loss after bariatric surgery are recognised causes of deficiency, and Wernicke's encephalopathy has been reported in these settings. The NIH fact sheet lists alcohol dependence, bariatric surgery, and malabsorption among the main risk groups, which is why clinicians ask about intake history when neurological symptoms appear.
Further reading
Summarised from published literature for reference only, with citations to the source. Evidence is graded as reported and is not a recommendation to combine, dose, or use any compound.
For personal tracking and education only. Not medical advice, diagnosis, or treatment, and not a medical device. Peptides may be prescription-only or unapproved where you live. Consult a licensed healthcare professional.