Vitamin B9 Supplement Pregnancy: Folic acid deficiency during pregnancy may lead to foetal malformations; harmful effects in the human foetus, mother or pregnancy have not been reported following ingestion of folic acid. Excreted in breast milk with no adverse effects observed in breast-fed infants.

Folic Acid

Brand names: Folic Acid Tablets (various generic)

Used in: Anaemia

Folic acid is synthetic folate used before and in early pregnancy to prevent neural-tube defects, to treat folate-deficiency anaemia, and alongside some drugs such as methotrexate.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 5 mg daily

Route: Oral

Frequency: Once daily

General medicine context. Folate-deficient megaloblastic anaemia (adults): 5 mg daily for 4 months. Up to 15 mg daily may be necessary in malabsorption states. Prophylaxis in chronic haemolytic states or renal dialysis: 5 mg every 1-7 days depending on diet and underlying disease. Drug-induced folate deficiency: 5 mg daily. Prevention of recurrence of neural tube defects: 5 mg daily starting before conception and continuing throughout the first trimester of pregnancy. Paediatric: over 1 year, as adult dose; up to 1 year, 500 micrograms/kg daily.

Paediatric dose

Dose: 0.5 mg/kg

Route: Oral

Frequency: Once daily

Source states 500 micrograms/kg daily for infants up to 1 year (0.5 mg/kg/day). Over 1 year: as adult dose. Verify against a children's formulary.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

Patient weight (kg)

Source states 500 micrograms/kg daily for infants up to 1 year (0.5 mg/kg/day). Over 1 year: as adult dose. Verify against a children's formulary.

Verify in a children's formulary

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION: Adults (persons over 12 years of age), One (1) capsule daily, between meals, or as prescribed by a physician. Do not exceed recommended dosage. Do not administer to children under the age of 12.

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2022-11-08. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Patients with malignant disease, unless megaloblastic anaemia is due to folic acid deficiency

Side effects

May worsen symptoms of co-existing vitamin B12 deficiency (should never be used to treat anaemia without full investigation of the cause)
Allergic reactions (rare): erythema, rash, pruritus, urticaria, dyspnoea, anaphylactic reactions including shock
Abdominal distension
Flatulence
Anorexia and nausea

Interactions

Sulfasalazine - may reduce absorption of folic acid
Cholestyramine - may interfere with folic acid absorption; take folic acid 1 hour before or 4-6 hours after cholestyramine
Anticonvulsants (phenytoin, phenobarbital, primidone) - serum levels may be reduced by folate; monitor and adjust anticonvulsant dose
Trimethoprim or sulfonamides / co-trimoxazole - may reduce the effect of folic acid (serious in megaloblastic anaemia)
Fluorouracil - fluorouracil toxicity may occur; avoid the combination
Antacids containing aluminium or magnesium - may reduce folic acid absorption; take antacids at least 2 hours after folic acid

Clinical monograph

How it works

It replaces folate, an essential cofactor for DNA synthesis and red-cell production.

Prescribing in practice

In macrocytic anaemia, exclude or treat vitamin B12 deficiency first — folate alone can mask B12 deficiency and allow neurological damage to progress.
Higher pre-conception doses are advised for pregnancies at increased risk of neural-tube defects.
With methotrexate, folic acid is taken on separate, specified day(s) — not on the methotrexate day.

Monitoring

Review the blood count and response; check B12 status where megaloblastic anaemia is being treated.

Counselling the patient

If planning pregnancy, start it before conception and continue through early pregnancy.
With methotrexate, take it only on the day(s) advised.

Evidence & guidelines

Pre-conception and early-pregnancy folate reduces neural-tube defects (standard antenatal guidance).

Reference: NICE NG201 (Antenatal Care); NICE NG23; BSH Haematology Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways