Thiamine (vitamin B1)

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

Thiamine helps to turn food into energy and 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.

Synthetic 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's sometimes also used to treat children with rare conditions like maple syrup urine disease and congenital lactic acidosis. A specialist doctor will need to prescribe it for them.

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

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

Most adults and children aged 12 years old and over can take thiamine.

Only give thiamine to a child under 12 years old 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 to take thiamine if you:

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

Thiamine comes as tablets containing 50mg or 100mg of thiamine. It also comes as slow-release tablets containing 100mg of thiamine and as a liquid containing 100mg in 5ml.

Your dose depends on why you need thiamine and whether it's 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.

Dose for children

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

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.

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.

If a doctor has prescribed thiamine to treat a vitamin B1 deficiency, you need to keep taking it until your levels have increased to normal again and your symptoms are better.

Many people who become deficient in vitamin B1 cannot absorb enough of the vitamin from their normal diet. They may need to continue taking a low dose of thiamine for a long time to prevent them from becoming deficient again.

The doctor will advise you on how much to take and how long for.

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

Missing 1 or 2 doses 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 at the usual time.

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.

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.

There are things you can do to help cope with these common side effects of thiamine:

Take thiamine with, or just after, a meal or snack. It may also help if you avoid rich or spicy food.

Drink lots of fluids, such as water or squash, to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee.

If you take the combined contraceptive pill or progestogen-only pill and you have severe diarrhoea for more than 24 hours, your contraception may not protect you from pregnancy. Check the pill packet for advice.

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 stomach may also help.

Speak to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or does not go away.

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

Call 999 now if:

• your lips, mouth, throat or tongue suddenly become swollen
• you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
• your throat feels tight or you're struggling to swallow
• your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
• you suddenly become very confused, drowsy or dizzy
• someone faints and cannot be woken up
• a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)

You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.

These can be signs of a serious allergic reaction and may need immediate treatment in hospital.

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

Thiamine can be taken during pregnancy. However, only take it if your doctor has recommended or prescribed it for you.

You can usually take thiamine while you are breastfeeding. However, only take it if your doctor has recommended or prescribed it for you.

If you have low thiamine levels, it's important that this is treated so that your milk contains enough thiamine for your baby.

Because thiamine is a natural part of breast milk, it's unlikely to cause any side effects in your baby even when it's taken as a supplement.

If you notice your baby is not feeding as well as usual, or you have any other concerns about your baby, talk to your doctor, pharmacist, health visitor or midwife.

There's no evidence that thiamine affects fertility in either men or women.

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 taking fluorouracil, a medicine used to treat some types of cancer.

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

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.

Tell your doctor or pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.