Section 18 · Monograph
Folic acid
Reviewed Nov 2026FDA label
FolateVitamin
- Forms
- Tab: 0.4, 0.8, 1mg
- Dose
- Women of childbearing age on antiepileptics: 0.4-4mg/day (higher doses per specialist/obstetric guidance)
- MOA
- Cofactor for nucleotide synthesis, ↓neural tube defect risk
Indications
- Megaloblastic anemia due to folate deficiencyFDA-labeled
- Prevention of neural tube defects in women of childbearing potentialFDA-labeled
Off-Label Uses
- Reduction of antiepileptic drug-related teratogenic risk (guidelines vary; commonly 0.4-4mg/day, with higher doses sometimes used with valproate or carbamazepine)Off-label
Mechanism of Action
- Cofactor for one-carbon transfer reactions required for nucleotide synthesis; reduces neural tube defect risk
Full Dosing
Adult / usual
- Women on antiepileptics who may become pregnant: 0.4-4mg/day starting before conception and through the first trimester (higher doses per specialist or obstetric guidance; evidence is mixed)
- Folate deficiency anemia: 1mg daily, up to 5mg/day as needed
Contraindications
- Pernicious anemia untreated with vitamin B12 (folate may mask hematologic signs while neurologic damage progresses)
- Known hypersensitivity
Drug Interactions
- Phenytoin, phenobarbital, primidone and valproate lower folate levels; high-dose folic acid may lower phenytoin levels — monitor seizure control
- Methotrexate and trimethoprim antagonize folate
Adverse Effects
- Generally well tolerated; rare allergic reactions
- High doses can mask vitamin B12 deficiency
- May lower antiepileptic drug levels (notably phenytoin)
Monitoring Parameters
- Folate and B12 status
- Anticonvulsant levels when starting high doses
- Seizure control
Pregnancy & Lactation
- Recommended before conception and during early pregnancy
- Compatible with breastfeeding