Vitamin B9 Pregnancy: Folic acid deficiency during pregnancy may lead to foetal malformations, and imbalance in folate-requiring trophoblast cells may lead to placental detachment. Very high doses have caused foetal abnormalities in rats, but harmful effects in the human foetus, mother or pregnancy have not been reported following ingestion of folic acid. Folic acid is excreted in breast milk; no adverse effects have been observed in breast-fed infants whose mothers were receiving folic acid.

Folic acid

Brand names: Lexpec

Folic acid is a synthetic form of vitamin B9 used to treat and prevent folate-deficiency anaemia and, in higher doses, 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: Folate-deficient megaloblastic anaemia: 5 mg daily for 4 months. Up to 15 mg daily may be necessary for malabsorption states.

Route: Oral (tablets)

Frequency: Once daily

Max: Up to 15 mg daily may be necessary for malabsorption states (highest dose stated in §4.2)

Source: eMC SPC for Folic Acid 5 mg Tablets, §4.2. Other indications: prophylaxis in chronic haemolytic states or in 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. SAFETY (§4.4): folic acid must not be given for pernicious anaemia or undiagnosed megaloblastic anaemia without sufficient cyanocobalamin (vitamin B12), as folic acid alone will not prevent — and may precipitate — subacute combined degeneration of the spinal cord; make a full clinical diagnosis before starting treatment. Folate should not be routinely used in patients receiving coronary stents. Caution in patients who may have folate-dependent tumours. Folic acid is removed by haemodialysis. The US cross-check label in the bundle is a combination product (Integra F — folic acid with ferrous fumarate and other ingredients, one capsule daily), so its dosing was NOT used for this single-ingredient page.

Paediatric dose

Dose: 500 micrograms/kg

Route: Oral

Frequency: Daily

eMC §4.2 verbatim: 'Paediatric population — Over 1 year: As adult dose. Up to 1 year: 500 µg/kg daily.' The per-kg figure recorded here (500 micrograms/kg daily, i.e. 0.5 mg/kg daily) applies to infants up to 1 year; children over 1 year take the adult dose, which is not a per-kg regimen. Verify all under-18 dosing against a children's formulary before prescribing.

Dose adjustments

Renal

No renal dose-reduction table is given. For prophylaxis in renal dialysis (and in chronic haemolytic states) the stated regimen is 5 mg every 1–7 days depending on diet and underlying disease. Folic acid is removed by haemodialysis (§4.4).

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)

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 due to folic acid deficiency is present

Side effects

Generally well tolerated
May worsen the symptoms of co-existing vitamin B12 deficiency — never use to treat anaemia without full investigation of the cause
Rare allergic reactions comprising erythema, rash, pruritus and urticaria
Rare dyspnoea and anaphylactic reactions (including shock)
Gastrointestinal: abdominal distension, flatulence, anorexia and nausea

Interactions

Sulfasalazine — may reduce the absorption of folic acid
Cholestyramine — may interfere with folic acid absorption; on prolonged cholestyramine therapy take folic acid 1 hour before or 4 to 6 hours after cholestyramine
Trimethoprim or sulfonamides, alone or combined as co-trimoxazole — may reduce the effect of folic acid, which may be serious in patients with megaloblastic anaemia
Anticonvulsants (phenytoin, phenobarbital, primidone) — serum levels may be reduced by folate administration; monitor carefully and adjust the anticonvulsant dose as necessary
Fluorouracil — fluorouracil toxicity may occur in patients taking folic acid; this combination should be avoided
Edible clay and antacids containing aluminium or magnesium — may reduce folic acid absorption; take antacids at least two hours after folic acid. Folic acid may also reduce intestinal absorption of zinc (of particular importance in pregnancy). Antibiotics may interfere with the microbiological assay for serum and erythrocyte folate, causing falsely low results.

Clinical monograph

How it works

It is converted to tetrahydrofolate, a cofactor in single-carbon transfer reactions essential for purine and pyrimidine synthesis and therefore for DNA synthesis and normal cell division.

Prescribing in practice

Folic acid can correct the anaemia of vitamin B12 deficiency while allowing neuropathy to progress, so vitamin B12 deficiency must be excluded or treated before giving folate for macrocytic anaemia.
Women planning pregnancy and those at higher risk of neural tube defects require appropriate preconception and early-pregnancy folate dosing.
It is not used as the sole treatment in pernicious anaemia where the underlying problem is B12 deficiency.

Monitoring

Monitor the haematological response with a full blood count and ensure vitamin B12 status has been assessed in macrocytic anaemia.

Counselling the patient

Folic acid is especially important before and during early pregnancy.
Take it regularly as advised even if you feel well.
Tell your clinician if you are also being investigated for low vitamin B12.

Evidence & guidelines

NICE recommends folic acid before conception and in the first trimester to reduce neural tube defect risk, with higher doses for higher-risk pregnancies.

Reference: NICE CG62; UKMI; 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