Thiamine (vitamin B1)

Pronunciation: THY-uh-min.

Generic name
thiamine (vitamin B1)
Drug class
Water-soluble B-complex vitamin / essential nutrient
Form
Tablets, capsules, oral solution, or injection
Route
Oral (tablet, capsule, or solution) or injection (intramuscular or intravenous)
Legal status
Available without a prescription as an oral dietary supplement in ordinary doses; prescription-only as an injectable treatment for diagnosed deficiency.

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: Thiamine Sterop (7) · Full directory

What thiamine (vitamin B1) is and how it works

Thiamine (vitamin B1) is an essential nutrient the body needs to turn food into energy. Most people get enough from a normal diet or a standard multivitamin. At prescription strength, injectable thiamine treats diagnosed deficiency, including serious conditions like beriberi and Wernicke's encephalopathy. (1) (2)

If you are taking thiamine as part of your everyday diet or an ordinary multivitamin, it is very safe. If a prescriber has recommended prescription-strength or injectable thiamine, this usually means a real deficiency has been found or is strongly suspected -- for example after heavy, long-term alcohol use, poor nutrition, or weight-loss (bariatric) surgery. Follow your prescriber's dosing exactly; injectable doses are individually decided, not a fixed number for everyone.

Mechanism of action: how thiamine (vitamin B1) works

Thiamine is converted in the body to thiamine pyrophosphate (TPP), a cofactor required for glycolysis, the Krebs cycle, and the pentose phosphate pathway, supporting carbohydrate, lipid, and amino-acid metabolism. (2) (1)

What thiamine (vitamin B1) is used for

Everyday nutritional support (oral supplement)

Used as an ordinary dietary supplement to help meet the body's daily need for vitamin B1, particularly if diet alone may be insufficient. (3)

Treatment of diagnosed thiamine deficiency, beriberi, and Wernicke-Korsakoff syndrome

Prescription-strength (often injectable) thiamine treats diagnosed thiamine deficiency, including beriberi (a deficiency disease affecting the heart and nerves) and Wernicke's encephalopathy or Wernicke-Korsakoff syndrome, a serious brain condition classically linked to chronic alcohol use, severe malnutrition, or malabsorption (including after bariatric surgery). It is also used for severe vomiting in pregnancy (neuritis of pregnancy) when this prevents adequate oral intake, and to help prevent Wernicke's encephalopathy when a person with marginal thiamine status is given intravenous dextrose (sugar) fluids. (1) (2) (4)

Before taking thiamine (vitamin B1)

Do not take / not appropriate for

  • Do not take thiamine (in any form) if you have had an allergic reaction to thiamine or any ingredient in the specific product. (all countries) (1) (4)

Tell your clinician about

  • Any previous allergic reaction to thiamine or a B-vitamin injection, including a reaction described as sneezing, mild asthma, or swelling.
  • Whether you have kidney problems, especially before any long-term injectable thiamine, because some injectable products contain aluminium that can build up if kidneys are impaired.
  • A history of heavy or long-term alcohol use, poor nutrition, malabsorption, or bariatric surgery, since these raise the chance of a real thiamine deficiency needing treatment.
  • All other medicines and supplements you take, including diuretics ('water tablets') and macrolide antibiotics.
  • Pregnancy, plans for pregnancy, or breastfeeding.
(1) (2)

How to take thiamine (vitamin B1)

  • For everyday supplement use, take oral thiamine as directed on the product label or by your prescriber.
  • For prescription-strength or injectable thiamine, the dose, route, and duration are individually decided by your prescriber based on how deficient you are and how you respond -- this is not a fixed dose for everyone.
  • Injectable thiamine is given by, or under the direct supervision of, a healthcare professional in a setting with facilities to treat a severe allergic reaction, because of a rare but real anaphylaxis risk.
  • If you are being given intravenous glucose or dextrose fluids and you are at risk of thiamine deficiency (for example from heavy alcohol use, malnutrition, or malabsorption), your clinical team will normally give or have already given you thiamine before or together with the glucose -- this specific order matters because glucose alone can trigger or worsen Wernicke's encephalopathy in a thiamine-deficient person.
(1) (2)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6) (7) (8)

Missed dose

For an everyday oral supplement, take a missed dose when you remember unless it is nearly time for your next one, in which case skip the missed dose -- do not take a double dose to catch up. For a prescription injectable course, contact your prescriber or clinic for specific guidance, since this depends on your individual treatment plan.

Overdose

Ordinary oral thiamine has no established toxic dose because the body excretes excess through the kidneys. If you suspect a very large accidental dose, or if anyone develops signs of a severe allergic reaction after an injection (such as facial or throat swelling, difficulty breathing, or widespread hives), seek emergency medical help immediately. (2) (1)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Oral thiamine at ordinary doses is very well tolerated, with side effects being rare.

What to notice: Oral thiamine at ordinary doses is very well tolerated, with side effects being rare.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

With injections: warmth, itching, mild rash, or injection-site discomfort.

What to notice: With injections: warmth, itching, mild rash, or injection-site discomfort.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1) (4)

Serious warnings

Signs of a severe allergic (anaphylactic) reaction to an injection — emergency

Symptoms: Swelling of the face, lips, tongue, or throat; tightness in the throat; difficulty breathing; widespread hives or rash; sneezing or mild wheeze can be an early warning sign.

Action: Seek emergency medical help immediately. This is a rare but real, sometimes fatal, reaction that has occurred with injected thiamine, especially after repeated injections -- which is why injectable thiamine is given in a setting equipped to treat anaphylaxis. (1) (4)

Suspected Wernicke's encephalopathy in someone at risk (e.g. chronic alcohol use, malnutrition, malabsorption) — emergency

Symptoms: Confusion, unsteady walking (ataxia), or abnormal eye movements.

Action: This is a medical emergency; a clinician will typically give thiamine urgently, and if intravenous glucose is also needed, thiamine is given before or together with it to avoid triggering or worsening the condition. (2) (1)

Interactions

  • Loop diuretics ('water tablets' such as furosemide) can increase how much thiamine is lost in urine. (2)
  • Macrolide antibiotics (such as erythromycin) may reduce thiamine transport into cells. (2)
  • Patiromer (a potassium-binding medicine) can reduce absorption of oral thiamine. (2)
  • The pyridoxine (vitamin B6) in some combination B-vitamin injections (such as Pabrinex) may interfere with the effects of levodopa (a Parkinson's disease medicine). (4)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Thiamine needs are higher in pregnancy, and thiamine is a normal, needed nutrient throughout pregnancy at ordinary doses. Prescription-strength or injectable thiamine in pregnancy (for example for severe vomiting) should be used under a prescriber's guidance, weighing benefits and any uncertain risks. (1) (2) (3) (4) (5) (6) (7) (8)

Breastfeeding

Thiamine is a normal, needed nutrient during breastfeeding at ordinary doses. It is not known whether injectable thiamine passes into breast milk in clinically significant amounts; discuss prescription-strength use with your prescriber. (1) (2) (3) (4) (5) (6) (7) (8)

Children

Oral thiamine is a normal part of a child's diet. Injectable thiamine for deficiency in children is a clinician-directed decision based on the specific condition being treated. (1) (2) (3) (4) (5) (6) (7) (8)

Elderly

No specific age-based dose adjustment is described in the sources reviewed, but older adults have a higher risk of underlying deficiency and are monitored accordingly. (1) (2) (3) (4) (5) (6) (7) (8)

Hepatic_impairment

No specific dose adjustment described in the sources reviewed for liver impairment. (1) (2) (3) (4) (5) (6) (7) (8)

Renal_impairment

Some injectable thiamine products contain aluminium, which may reach toxic levels with prolonged use if kidney function is impaired -- tell your prescriber about any kidney problems before a prolonged injectable course. (1) (2) (3) (4) (5) (6) (7) (8)

Source_ids

US-DAILYMED-THIAMINE-INJ-2026,US-NCBI-STATPEARLS-THIAMINE-2026,US-NIH-ODS-THIAMIN-HP-2026 (1) (2) (3) (4) (5) (6) (7) (8)

Monitoring

Before starting

  • Assessment of deficiency risk factors (alcohol use, nutrition, malabsorption, bariatric surgery history)
  • Kidney function where prolonged injectable use with aluminium-containing products is planned

During treatment

  • Clinical response (resolution of symptoms such as confusion, unsteadiness, or heart-related signs of beriberi).
  • Laboratory measures of thiamine status where available (e.g. erythrocyte transketolase activity or erythrocyte thiamine pyrophosphate level), used by the clinical team rather than at home.
  • Watching for signs of an allergic reaction during and shortly after each injection.
(2) (1)

Storage

Store oral thiamine products at room temperature as directed on the label, away from moisture. Injectable thiamine products are stored and prepared by pharmacy or clinical staff according to the specific product's instructions.

Professional information

Clinician-facing context only, sourced from the current US FDA prescribing information for injectable thiamine and NIH/NCBI clinical references; verify against the current full label and local guidance before prescribing.

United States

Indication: Beriberi, Wernicke-Korsakoff syndrome, neuritis of pregnancy, and prevention of Wernicke's when giving IV dextrose to an at-risk patient

Dose summary: Beriberi: 10-20 mg IM three times daily up to 2 weeks, then oral maintenance. Wernicke-Korsakoff syndrome: initial 100 mg IV, then 50-100 mg IM daily until a regular diet resumes. Neuritis of pregnancy: 5-10 mg IM daily. IV dextrose prophylaxis in at-risk patients: 100 mg thiamine hydrochloride added to each of the first few litres of IV fluid, given before or with the glucose.

Renal context: Caution with prolonged parenteral use in renal impairment because of aluminium content in some products; specific dose adjustment not established in the source reviewed. (1)

Mechanism of action

Hepatic guidance

No specific hepatic dosing guidance described in the sources reviewed.

Overdose note

No established toxicity ceiling for thiamine; excess is renally excreted. The main serious risk with parenteral administration is rare anaphylaxis rather than dose-related toxicity. (2) (1)

Frequently asked questions

Is thiamine (vitamin B1) available in the US, UK, Europe, Canada, Australia, and New Zealand?

Yes. It is available as an everyday oral supplement essentially everywhere, and a regulator-approved prescription injectable form is confirmed in all of these markets. (1) (5) (4) (6) (7) (8)

Why does thiamine need to be given before glucose in some patients?

In someone who is thiamine-deficient (for example from chronic heavy alcohol use, malnutrition, or malabsorption), giving intravenous glucose (sugar) can use up the body's remaining thiamine stores and trigger or worsen Wernicke's encephalopathy, a serious brain condition. This is why clinical teams give thiamine before or together with IV glucose in at-risk patients. (2) (1)

Is thiamine safe to take every day as a supplement?

Yes, at ordinary supplement doses thiamine is very safe, with no established upper toxicity limit because the body excretes excess through the kidneys. The rare, more serious risks (such as anaphylaxis) relate specifically to injected, prescription-strength thiamine, not everyday oral supplement use. (2)

What is the mechanism of action of thiamine (vitamin B1)?

Thiamine is converted in the body to thiamine pyrophosphate (TPP), a cofactor required for glycolysis, the Krebs cycle, and the pentose phosphate pathway, supporting carbohydrate, lipid, and amino-acid metabolism. (2) (1)

What is the generic name of Thiamine (vitamin B1)?

The generic name is thiamine (vitamin B1). (1) (2) (3)

What class of drug is thiamine (vitamin B1)?

Thiamine (vitamin B1) is classed as: Water-soluble B-complex vitamin / essential nutrient. (1) (2) (3)

References

  1. Thiamine Hydrochloride Injection, USP -- full prescribing informationU.S. Food and Drug Administration / DailyMed (NIH), full prescribing information for Thiamine Hydrochloride Injection, USP · United States · dated 2026-01-01 · accessed 2026-07-29 · source 1
  2. Vitamin B1 (Thiamine)National Library of Medicine / NCBI Bookshelf, StatPearls (peer-reviewed clinical reference) · United States · dated 2025-01-01 · accessed 2026-07-29 · source 2
  3. Thiamin -- Health Professional Fact SheetNIH Office of Dietary Supplements (ODS), Thiamin -- Health Professional Fact Sheet · United States · dated 2023-02-09 · accessed 2026-07-29 · source 3
  4. Pabrinex Intravenous High Potency, Concentrate for Solution for Infusion -- SmPCelectronic medicines compendium (emc), United Kingdom -- Summary of Product Characteristics for Pabrinex Intravenous High Potency (contains thiamine hydrochloride) · United Kingdom · dated 2026-01-01 · accessed 2026-07-29 · source 4
  5. BEVITINE 100 mg/2 mL, solution injectable en ampouleBase de donnees publique des medicaments (France) / ANSM-authorised product information for Bevitine (thiamine hydrochloride injectable) -- representative of EU member-state authorisation · European Union · dated 2026-01-01 · accessed 2026-07-29 · source 5
  6. Thiamine Hydrochloride Injection, USP -- DPD product record (DIN 02243525)Health Canada Drug Product Database (DPD) · Canada · dated 2015-09-14 · accessed 2026-07-29 · source 6
  7. THIAMINE STEROP thiamine hydrochloride 100 mg/2 mL solution for injection ampoule -- ARTG entryTherapeutic Goods Administration (TGA), Australia · Australia · dated 2024-07-10 · accessed 2026-07-29 · source 7
  8. Thiamine Sterop 100 mg/2 mL solution for injection -- New Zealand Data SheetMedsafe (New Zealand regulator) · New Zealand · dated 2026-01-01 · accessed 2026-07-29 · source 8

Brand names by country

Single-ingredient thiamine (vitamin B1) names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • Thiamine Hydrochloride Injection, USP (generic) (1)FDA approved currently labeled · 100 mg/mL · multiple generic manufacturers

United Kingdom

  • Pabrinex Intravenous High Potency (combination product containing thiamine) (4)MHRA licensed emc smpc confirmed · 250 mg thiamine hydrochloride per ampoule pair · Alissa Healthcare Research Ltd

Canada

  • VITAMIN B1
  • THIAMINE HCL INJ
  • THIAMIJECT INJECTION - LIQ IM IV
  • BETAXIN

Australia

  • Thiamine Sterop (7)TGA ARTG registered confirmed · 100 mg/2 mL · Boucher & Muir Pty Ltd

New Zealand

  • Thiamine Sterop (8)Medsafe approved confirmed · 100 mg/2 mL · Sterop
View brands in additional countries.

European Union

Bevitine (France, representative EU member-state authorisation) (5)

This page provides general reference information about thiamine (vitamin B1) and is not a substitute for advice from a prescriber, pharmacist, or dietitian managing your care. All prescription-strength and injectable dosing decisions should be made with your prescriber.

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