Can I take thiamine (vitamin B1) while pregnant or breastfeeding?
A plain-words look at what the NHS, the US drug label and LactMed say about thiamine (vitamin B1).
In short
Pregnancy: Thiamine can be taken in pregnancy, but only if your doctor has advised you to take it or prescribed it.
Breastfeeding: You can usually take thiamine while breastfeeding, but only if your doctor has advised you to take it or prescribed it.
Your doctor, midwife or pharmacist can help you decide.
What this means for you
Breastfeeding
- If your thiamine levels are low, it's important to have this treated so that your breast milk has enough thiamine for your baby.
- Thiamine is naturally found in breast milk, so it's unlikely to cause side effects in your baby, even when you take it as a supplement.
- Speak to your doctor, pharmacist, health visitor or midwife if your baby is feeding less well than normal, or if anything else about your baby worries you.
Talk to your doctor or pharmacist
This page is educational, not advice for your own situation. Talk to your doctor, midwife or pharmacist before you start, stop or change any medicine in pregnancy or while breastfeeding.
The details: what each source says
Thiamine (vitamin B1) in pregnancy
The NHS says
Thiamine can be taken in pregnancy, but only if your doctor has advised you to take it or prescribed it.
In our words, from the NHS page Thiamine (vitamin B1) (nhs.uk). Contains public sector information licensed under the Open Government Licence v3.0 (OGL v3.0). The NHS does not endorse this site.
Thiamine (vitamin B1) while breastfeeding
The NHS says
You can usually take thiamine while breastfeeding, but only if your doctor has advised you to take it or prescribed it.
If your thiamine levels are low, it's important to have this treated so that your breast milk has enough thiamine for your baby.
Thiamine is naturally found in breast milk, so it's unlikely to cause side effects in your baby, even when you take it as a supplement.
Speak to your doctor, pharmacist, health visitor or midwife if your baby is feeding less well than normal, or if anything else about your baby worries you.
In our words, from the NHS page Thiamine (vitamin B1) (nhs.uk). Contains public sector information licensed under the Open Government Licence v3.0 (OGL v3.0). The NHS does not endorse this site.
The US prescribing label says
Nursing Mothers It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when thiamine hydrochloride is administered to a nursing mother.
Prescribing label, section “Nursing Mothers”: Thiamine Hydrochloride (intramuscular, intravenous), REMEDYREPACK INC. Label on DailyMed. Quoted verbatim; US labels are written for US prescribers and patients.
This quote is from the intramuscular/intravenous formulation label.
Other names
UK brand names (per the NHS): Benerva, Tyvera, Athiam, ThiaDose, ThiamEss.
US name: thiamine.
Sources
- NHS, Thiamine (vitamin B1) (nhs.uk), page last reviewed 9 February 2023. Paraphrased. Contains public sector information licensed under the Open Government Licence v3.0.
- US drug label: Thiamine Hydrochloride (intramuscular, intravenous), REMEDYREPACK INC., human prescription drug, label effective 31 August 2026, set ID 0f38c4ba-cebf-49f4-b0a6-8a5d3ebf618c. DailyMed (National Library of Medicine). Public domain; quoted verbatim.
Sources checked 26 September 2026. How we source and check every page.
Educational summary of named sources, not medical advice.