Thiamine (vitamin B1)

1. About thiamine

Thiamine, also known as thiamin or vitamin B1, is one the of B vitamins.

Thiamine helps to turn food into energy to keep the nervous system healthy. Your body is not able to make thiamine for itself. However, you can usually get all you need from your food.

Man-made thiamine can be used to treat or prevent vitamin B1 deficiency (this is when you do not have enough of this vitamin in your body).

It is sometimes also used to treat to children with rare conditions like maple syrup urine disease and congenital lactic acidosis. It will be prescribed to them by a specialist doctor.

You can get thiamine on prescription. It comes as standard-release and slow-release tablets. For severe vitamin B deficiency it comes as an injection. However, this is usually given in hospital.

You can buy thiamine supplements from pharmacies, supermarkets and other shops. These include vitamin B complex tablets and multivitamin tablets where thiamine is listed as an ingredient.

2. Key facts

  • You'll usually take thiamine once a day if you have a mild vitamin B1 deficiency.
  • You can take it with or without food.
  • It's best to avoid alcohol if you are taking thiamine for a vitamin B1 deficiency.
  • Some people may feel sick or have a stomach ache when taking thiamine, but these side effects are usually mild.
  • Thiamine is also called by the brand names Benerva and Tyvera.

3. Who can and can't take thiamine

Most adults and children aged 12 years or older can take thiamine.

Only give thiamine to a child under the age of 12 years if a specialist recommends it.

Thiamine may not be suitable for some people. To make sure it's safe for you, tell your doctor before starting thiamine if you:

  • have had an allergic reaction to thiamine or any other medicine in the past
  • are due to have any blood tests or scans thiamine – can affect the results of certain tests

4. How and when to take it

If you or your child have been prescribed thiamine, follow the doctor's instructions when taking it.

If you have bought thiamine from a pharmacy or a shop, follow the instructions that come with the packet.

How much will I take?

The dose will vary depending on why you need thiamine and whether it has been prescribed by a doctor.

Mild thiamine deficiency – the usual dose for adults is between 25mg and 100mg, taken once a day.

Severe thiamine deficiency – the usual dose for adults is 100mg, taken 2 or 3 times a day.

If your child is prescribed thiamine, the doctor will use your child’s weight to work out the right dose.

How to take it

You can take thiamine with or without food.

Swallow the tablet whole with a drink of water. If you find tablets difficult to take, break the tablet in half using the line down the middle. Take both halves separately.

Will my dose go up or down?

For treating a vitamin B1 deficiency, your dose will usually stay the same until your levels are back to normal and your symptoms improve.

Once your levels are OK, your doctor will probably put you on a lower dose to make sure you do not become deficient again.

What if I forget to take it?

Missing 1 or 2 doses by mistake will probably not matter too much. But if you have a vitamin deficiency and you keep forgetting to take your thiamine, ask a doctor for advice.

If you forget to take your thiamine, take the missed dose as soon as you remember, unless it's nearly time for your next dose. In this case skip the missed dose and just take the next one as normal.

Do not take 2 doses to make up for a forgotten one.

If you forget doses often, it may help to set an alarm to remind you. You could also ask a pharmacist for advice on other ways to help you remember to take your medicine.

Speak to your doctor if you've been prescribed thiamine and you want to stop taking it for any reason.

What if I take too much?

Thiamine is generally a very safe medicine. Taking too much is unlikely to harm you or your child.

If you're worried, speak to a pharmacist or doctor.

5. Side effects

Like all medicines, thiamine can cause side effects in some people. But most people have no side effects or only minor ones.

Common side effects

Talk to a pharmacist or doctor if these side effects bother you or do not go away:

  • feeling sick (nausea)
  • diarrhoea
  • stomach ache

Serious allergic reaction

In rare cases, thiamine can cause a serious allergic reaction (anaphylaxis).

These are not the full side effects of thiamine. For a full list, see the leaflet inside your medicines packet.


You can report any suspected side effect to the UK safety scheme.

6. How to cope with side effects

What to do about:

  • feeling sick – take thiamine with, or just after, a meal or snack. It may also help if you avoid rich or spicy food.
  • diarrhoea – drink plenty of water to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee.
  • stomach ache – take your thiamine with, or just after a meal or snack. Some gentle movement or exercise may help any pain. Putting a heat pad or covered hot water bottle on your tummy may also help.

If your symptoms do not improve after a couple of days or get worse speak to a doctor.

7. Pregnancy and breastfeeding

Thiamine is generally safe to take during pregnancy. However, only take it if your doctor has recommended or prescribed it for you.

Thiamine and breastfeeding

Thiamine is usually safe to take while you're breastfeeding. It passes into your breast milk, but it's not harmful to your baby.

However, if your baby is premature or has health problems, check with a doctor before taking thiamine if you want to breastfeed.


Tell your doctor if you're trying to get pregnant, are already pregnant or if you're breastfeeding.

8. Cautions with other medicines

It's generally safe to take thiamine while you're taking other medicines.

However, check with a doctor before starting on thiamine if you're on fluorouracil, a medicine used to treat some types of cancer.

Fluorouracil can interfere with the way thiamine works. The doctor may need to adjust your dose of thiamine.

Mixing thiamine with herbal remedies or supplements

Talk to a pharmacist or doctor before taking any herbal remedies or supplements together with thiamine.

Some vitamin and mineral supplements may already contain thiamine. Always check the labels carefully.


For safety, tell a doctor or pharmacist if you're taking any other medicines, including herbal medicines, vitamins or supplements

9. Common questions

Page last reviewed: 28/11/2019
Next review due: 28/11/2022