Vitamin B1, or thiamine, is a water-soluble vitamin the body needs to turn carbohydrate into energy and to keep nerves working. It is used for diagnosed deficiency, nerve symptoms, and — importantly — in alcohol dependence, where deficiency can cause a medical emergency.
What is B1?
Vitamin B1 is thiamine. It is water-soluble, so the body stores very little — only a few weeks’ worth — and needs a regular supply.
Thiamine’s central job is energy metabolism. It is a co-factor for enzymes that convert carbohydrate into usable energy. Tissues that burn a lot of energy and depend heavily on glucose feel a shortage first — which means the brain, the nerves and the heart.
That explains what deficiency looks like:
- Dry beriberi — peripheral neuropathy: tingling, numbness, burning and weakness, typically starting in the feet.
- Wet beriberi — heart failure, breathlessness and swelling.
- Wernicke’s encephalopathy — a medical emergency causing confusion, unsteadiness and eye movement problems.
- Korsakoff syndrome — severe, often permanent memory damage, which can follow untreated Wernicke’s.
Deficiency is uncommon on a varied diet — thiamine is in whole grains, pork, legumes, nuts and fortified cereals — but it is far from rare in specific groups, and those are where it matters.
It is often taken as part of a B-complex, such as Neurobion, which combines B1, B6 and B12.
What is B1 commonly used for?
- Diagnosed thiamine deficiency.
- Alcohol dependence, where deficiency is common and consequential — alcohol impairs both absorption and use of thiamine, and intake is often poor.
- Preventing and treating Wernicke’s encephalopathy, where it is given urgently and usually by injection.
- Peripheral neuropathy, where thiamine deficiency is the cause.
- Beriberi, in either form.
- Malabsorption — after bariatric surgery, in coeliac disease, or with persistent vomiting.
- Heart failure, in some cases, particularly where long-term diuretic use has depleted it.
- Prolonged vomiting in pregnancy (hyperemesis gravidarum).
- Dialysis and critical illness.
The alcohol point
This is the use where getting it right changes outcomes.
In someone drinking heavily, thiamine stores are low and the reserve is small. Giving carbohydrate — a sugary drink, a meal, or intravenous glucose — without thiamine can precipitate Wernicke’s encephalopathy, because metabolising that glucose consumes the little thiamine left. In hospital, thiamine is given before or with glucose for exactly this reason.
Wernicke’s is a medical emergency and it is frequently missed. The full triad of confusion, unsteadiness and eye movement abnormalities often does not appear together — confusion alone is common. Untreated, it can progress to permanent memory damage. If someone who drinks heavily becomes confused or unsteady, that needs urgent medical attention, not a supplement from the shelf.
Oral thiamine is used for prevention and for mild deficiency; established or suspected Wernicke’s needs high-dose parenteral treatment in a hospital.
Who commonly looks for B1 and why
- People with tingling or numbness in the hands or feet.
- People who drink heavily, or their families.
- People on long-term diuretics, particularly furosemide, which increases thiamine loss.
- People after bariatric surgery, where deficiency is a recognised risk.
- People with persistent vomiting, including in pregnancy.
- People with diabetes, where thiamine status is sometimes lower.
- People taking a B-complex wanting to know what the B1 does.
- People with unexplained fatigue, hoping a B vitamin helps.
What to check on the label before taking B1
Check whether a combination product suits you better, or worse. If you are taking B1 for nerve symptoms, a B-complex may be more appropriate — but it will also contain B6, and sustained high B6 intake causes the nerve damage you are trying to treat. Check the B6 amount and add up every product you take. See Vitamin B6 Pyridoxine.
Thiamine itself has no established toxic level from supplements — excess is excreted — which makes it one of the safer vitamins to take. That is not a reason to take large amounts indefinitely without a purpose.
Speak to a pharmacist or doctor if:
- Alcohol is a factor. Do not manage this with an over-the-counter supplement alone; deficiency here can be serious and prevention should be medically supervised.
- Someone who drinks heavily is confused or unsteady — treat that as urgent.
- You have nerve symptoms that have not been diagnosed.
- You have had bariatric surgery, or have a malabsorption condition.
- You have persistent vomiting, including in pregnancy.
- You have heart failure or take long-term diuretics.
- You are pregnant or breastfeeding.
Safety, interactions and when to seek professional advice
Oral thiamine is well tolerated. It has no established upper limit from food or supplements, and side effects are uncommon.
But a supplement is not the answer to serious deficiency. Suspected Wernicke’s encephalopathy needs urgent hospital treatment with high-dose intravenous thiamine — oral tablets are not adequate and the delay matters. This is a genuine emergency where outcomes depend on speed.
Do not treat undiagnosed nerve symptoms with vitamins. Tingling and numbness have many causes — diabetes is the commonest, then B12 deficiency, thyroid disease, nerve compression, alcohol, HIV and TB medicines. Several are treatable, and some worsen if missed.
If you drink heavily, tell a doctor. Thiamine supplementation is part of managing that, and there is no judgement in asking. Stopping alcohol abruptly after heavy long-term use is itself dangerous and needs medical supervision.
Persistent fatigue deserves assessment rather than a supplement — anaemia, thyroid disease, diabetes, sleep apnoea and depression are common and treatable.
Seek urgent medical attention for confusion, unsteadiness or eye movement problems in someone who drinks heavily; for new, worsening or spreading numbness, tingling or weakness; for breathlessness with swollen legs; for memory problems developing over days or weeks; or for persistent vomiting preventing you from eating.
Related supplement guides
Frequently asked questions
What is vitamin B1 used for? Diagnosed thiamine deficiency, nerve symptoms caused by it, beriberi, and prevention of Wernicke’s encephalopathy — particularly in alcohol dependence.
Why is it important in alcohol dependence? Alcohol impairs thiamine absorption and use while intake is often poor. Deficiency can cause Wernicke’s encephalopathy, a medical emergency that may lead to permanent memory damage.
Can you take too much? Thiamine has no established toxic level from supplements — excess is excreted. That said, there is no benefit in large amounts without a reason.
Will it help my tingling feet? Only if thiamine deficiency is the cause. Diabetes and B12 deficiency are commoner causes, so get it diagnosed rather than assuming.
Is a B-complex better than B1 alone? Sometimes, since deficiencies often overlap. But check the B6 content — high B6 over time causes nerve damage, and stacking products is how people get there.
When is an injection needed instead of tablets? For suspected or established Wernicke’s encephalopathy, which needs urgent high-dose intravenous treatment in hospital. Tablets are not adequate there.