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Vitamin B group (folate) 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, Lexpec

Folic acid is a synthetic form of vitamin B9 used to treat and prevent folate-deficiency anaemia and to reduce the risk of neural tube defects in pregnancy.

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
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

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

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 is reduced to tetrahydrofolate, an essential cofactor for single-carbon transfer reactions underpinning purine and pyrimidine synthesis, DNA replication and normal cell division.

Prescribing in practice

  • Giving folic acid in unrecognised vitamin B12 deficiency can improve the blood picture while permitting irreversible neurological damage, so exclude or treat B12 deficiency first in macrocytic anaemia.
  • Preconception and early-pregnancy supplementation reduces neural tube defect risk, with higher doses for women at increased risk.
  • Folate alone does not treat the underlying defect in pernicious anaemia.

Monitoring

Confirm response with a full blood count and assess vitamin B12 status before treating a macrocytic anaemia with folate.

Counselling the patient

  • Begin folic acid before pregnancy where possible and continue through early pregnancy.
  • Continue taking it as directed even when you feel well.
  • Mention any concern about low vitamin B12 to your clinician.

Evidence & guidelines

NICE advises folic acid in the periconceptional period to lower neural tube defect risk, with increased doses for higher-risk pregnancies.

Reference: NICE PH11 Folic Acid; RCOG Green-Top; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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