A B-vitamin supplement (folate)
Folic acid
A B-vitamin used to prevent and treat folate-deficiency anaemia, to protect against neural-tube defects before and in early pregnancy, and to reduce side effects of methotrexate.
What is Folic acid?
Folic acid is a man-made form of folate (vitamin B9). It treats and prevents folate-deficiency anaemia, is taken before conception and in early pregnancy to reduce the risk of spina bifida and other neural-tube defects in the baby, and is used weekly alongside methotrexate to reduce its side effects. It is a well-tolerated tablet.
Education and reference only. This is a plain-language guide to Folic acid — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Folic acid is the supplement form of folate, a B-vitamin the body needs to make healthy red blood cells and to build and repair DNA. It has several distinct uses: correcting or preventing folate-deficiency anaemia; protecting a developing baby, when taken before conception and through the first 12 weeks of pregnancy, against neural-tube defects such as spina bifida; and, taken on a separate day from methotrexate, reducing that medicine’s side effects. It is a simple daily (or, with methotrexate, weekly) tablet.
How it works
Folate is essential for making the "building blocks" of DNA and for producing healthy red blood cells. When folate is lacking, the bone marrow makes large, poorly functioning red cells (megaloblastic anaemia). Folic acid replenishes the body’s folate, restoring normal blood-cell production. In early pregnancy, adequate folate is critical for the correct closure of the baby’s developing spine and brain, which is why supplementation before and in early pregnancy prevents many neural-tube defects.
What it treats
Conditions Folic acid is used for
Practical use
How to take Folic acid
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it as directed for your reason — daily for anaemia or pregnancy, or on a set day each week (different from the methotrexate day) if used with methotrexate.
- For pregnancy, take it from before conception (if possible) until the end of the 12th week; a higher amount is used if you are at increased risk.
- It can be taken with or without food.
- If you are being treated for anaemia, make sure vitamin B12 has been checked too — folic acid should not simply be taken alone for unexplained anaemia.
- It is very safe; simply resume as normal if you miss an occasional dose (do not double up).
Weighing it up
Advantages & disadvantages of Folic acid
Advantages
- Effectively prevents and treats folate-deficiency anaemia.
- Substantially reduces the risk of neural-tube defects when taken before and in early pregnancy.
- Reduces the side effects of methotrexate; inexpensive and very well tolerated.
Disadvantages
- Can mask vitamin B12 deficiency if taken alone for anaemia without checking B12 first.
- The pregnancy benefit depends on starting early — ideally before conception.
- Not a treatment for tiredness in people who are not actually folate-deficient.
Practical use
Good to know
The dose and timing depend on the reason for taking it. For pregnancy, it is taken from before conception (ideally) until the end of the first 12 weeks, at a standard amount for most women and a higher amount for those at greater risk (for example diabetes, epilepsy medicines, a previous affected pregnancy, or a high body weight). With methotrexate, folic acid is taken on a different day from the methotrexate dose. Importantly, in anaemia it is essential to check that the cause is folate deficiency and not vitamin B12 deficiency, because giving folic acid alone when B12 is low can mask the problem and, rarely, allow nerve damage to progress — so anaemia is investigated before treatment.
Who should not take it / use with caution
- People with untreated vitamin B12 deficiency, until B12 is also being addressed (to avoid masking it).
- People with certain folate-dependent cancers, without specialist advice.
- Otherwise it is suitable for almost everyone, including in pregnancy — indeed it is recommended then.
Monitoring
- Blood count (response of anaemia)
- Vitamin B12 checked before treating anaemia
- Usually none for pregnancy or methotrexate use
Side effects
- Very well tolerated — side effects are uncommon.
- Occasionally mild stomach upset or, rarely, an allergic reaction.
- No sedation or dependence.
Key interactions
- Some antiepileptic medicines (such as phenytoin) can lower folate levels, and folic acid can slightly affect phenytoin levels — this is managed by your prescriber.
- It works alongside methotrexate to reduce side effects (taken on a different day), not against it.
- Certain other medicines can reduce folate; a higher supplement amount may be advised.
Available as: Tablets (various strengths) and an oral liquid.
Answers
Folic acid: frequently asked questions
When should I start folic acid for pregnancy?
Ideally before you conceive and continuing until the end of the 12th week of pregnancy, because the baby’s spine and brain form very early — often before a pregnancy is confirmed. Most women take a standard amount; a higher amount is recommended for those at increased risk (for example with diabetes, certain epilepsy medicines, a higher body weight, or a previous affected pregnancy).
Why is folic acid taken on a different day from methotrexate?
Folic acid reduces methotrexate’s side effects (such as nausea and mouth ulcers) without stopping it working, but it is taken on a separate day so it does not blunt the methotrexate dose itself. Follow the specific days your team advises — for example methotrexate on one day and folic acid later in the week.
Can folic acid hide a vitamin B12 problem?
Yes — this is why unexplained anaemia should be investigated before treatment. Folic acid can correct the anaemia caused by low B12 while allowing B12-related nerve damage to progress unnoticed. So B12 is checked, and treated if low, rather than simply taking folic acid alone.
Will folic acid boost my energy if I’m tired?
Only if your tiredness is actually due to folate deficiency. Folic acid corrects a genuine shortage, but it is not a general energy supplement, and taking it will not help tiredness that has another cause. If you are persistently tired, it is worth having the cause investigated.
Authoritative sources
- BNF: Folic acid.
- electronic Medicines Compendium (SmPC): Folic acid.
- NICE CKS: Anaemia – B12 and folate deficiency; Pre-conception advice.
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