Haematology
Folic acid
Vitamin B9 (folate) — Prevents and treats folate deficiency — and protects against neural-tube defects in pregnancy.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
Quick answer
What is Folic acid?
Folic acid is a B vitamin essential for making DNA and healthy red blood cells. It is used to prevent neural-tube defects around conception, to treat folate-deficiency anaemia, and to reduce the side-effects of methotrexate.
- How it works: Folate is needed for cells to divide and to build the genetic material of new cells — including the rapidly dividing cells of a developing baby and the bone marrow making red blood cells.
- In practice: In practice folic acid has three everyday roles.
What it is
Folic acid is a B vitamin essential for making DNA and healthy red blood cells. It is used to prevent neural-tube defects around conception, to treat folate-deficiency anaemia, and to reduce the side-effects of methotrexate.
How it works
Folate is needed for cells to divide and to build the genetic material of new cells — including the rapidly dividing cells of a developing baby and the bone marrow making red blood cells. Supplying folic acid corrects or prevents the shortfall.
In practice
In practice folic acid has three everyday roles. First, in pregnancy planning: taken before conception and through early pregnancy it substantially reduces the risk of neural-tube defects such as spina bifida, with a higher dose advised for women at higher risk (for example with diabetes, on certain antiepileptics, with a previous affected pregnancy, or with a high body weight). Second, treating folate-deficiency anaemia. Third, as weekly cover alongside methotrexate to reduce its side-effects — taken on a different day from the methotrexate. A key safety principle is not to give folic acid alone when vitamin B12 deficiency is possible without also checking and treating the B12, because correcting the anaemia can mask continuing B12 deficiency and allow nerve damage to progress.
Examples
Practical use
How to take it & use it well
- If you are planning a pregnancy or could become pregnant, start taking folic acid before conception and continue through the early weeks of pregnancy, ideally once daily at the same time each day.
- It can be taken with or without food; if it upsets your stomach, taking it with a meal may help.
- If you take it as a weekly folate dose alongside methotrexate, take it on a different day from your methotrexate, not the same day.
- If you miss a daily dose, take it when you remember that day; do not double up to make up for a missed one.
- Store tablets in a cool, dry place out of reach of children, and keep taking them for as long as your clinician advises.
Common uses
- Before and during early pregnancy (neural-tube-defect prevention)
- Folate-deficiency anaemia
- Weekly cover with methotrexate
Monitoring
- Full blood count and folate (and B12) where treating deficiency
- Pregnancy-risk assessment to set the right preventive dose
- Response of anaemia
Weighing it up
Advantages & disadvantages
Advantages
- Taken around conception and in early pregnancy it greatly reduces the risk of neural-tube defects such as spina bifida in the baby.
- It effectively treats and prevents folate-deficiency anaemia.
- Taken alongside methotrexate it helps reduce some side effects of that medicine.
- It is inexpensive, well tolerated and available over the counter.
Disadvantages
- It does not correct a vitamin B12 deficiency and, if taken alone when B12 is low, can mask the anaemia while nerve damage progresses.
- Some people need a higher dose because of certain conditions, medicines or a previous affected pregnancy - this should be assessed by a clinician.
- It only helps when started early enough; beginning it after the first weeks of pregnancy misses the key window for preventing neural-tube defects.
- It is a supplement, not a substitute for a balanced diet and other recommended pregnancy care.
Key safety principles
What to watch for
- Do not treat with folic acid alone if vitamin B12 deficiency is possible — check and treat B12 too, or nerve damage can be masked.
- A higher pre-pregnancy dose is advised for women at higher risk of neural-tube defects.
- With methotrexate, take it on a different day (not the same day as the methotrexate).
Key interactions
What to avoid or check alongside
- Methotrexate works against folate, which is why folic acid is given on a separate day to reduce side effects without blocking the treatment.
- Some anti-epileptic medicines can lower folate levels and may interact, so tell your clinician what you take.
- Taking folic acid alone when vitamin B12 may be low can hide B12 deficiency and allow nerve problems to worsen - B12 should be checked first.
- Certain medicines that reduce folate absorption may mean you need a different dose or monitoring.
Patient & carer advice
- If you could become pregnant, start it before conception and continue through early pregnancy
- If you take methotrexate, take folic acid on a different day
- It is very safe, but tell us if you have had pernicious anaemia or B12 problems
Use with
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Answers
Folic acid: frequently asked questions
When should I start taking folic acid if I want to get pregnant?
Ideally before you conceive and through the first weeks of pregnancy, as this is when it protects against neural-tube defects. Start as soon as you begin trying.
Do I need a higher dose of folic acid?
Some people do - for example with certain medical conditions, some medicines, or a previous pregnancy affected by a neural-tube defect. Ask your GP or midwife to advise on the right dose for you.
Why can't folic acid be taken alone if my B12 might be low?
Folic acid can improve the blood picture of anaemia while leaving a B12 deficiency untreated, allowing nerve damage to continue. Your clinician will check B12 before treating with folic acid alone.
Can I take folic acid on the same day as my methotrexate?
No. When a weekly folate dose is used with methotrexate it should be taken on a different day, so it does not interfere with how methotrexate works.
Is folic acid safe to take in pregnancy?
Yes, it is recommended in pregnancy and is considered safe at the doses advised. Follow the dose your midwife or GP recommends.
Authoritative sources
Always verify against the source
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