Formulary
Folic Acid: Uses, Dosing, Side Effects and Indian Brand Names
Folic acid is essential for DNA synthesis and neural tube development. Periconceptional supplementation reduces neural tube defects by 50-70%. It must not be given alone in suspected B12 deficiency as it corrects anaemia but masks progressive neurological damage.
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Folic Acid: Uses, Dosing, Side Effects and Indian Brand Names
Folic acid is essential for DNA synthesis and neural tube development. Periconceptional supplementation reduces neural tube defects by 50-70%. It must not be given alone in suspected B12 deficiency as it corrects anaemia but masks progressive neurological damage.
NEET PG High-Yield: Folic acid corrects ANAEMIA of B12 deficiency but NOT the NEUROPATHY -- this masking effect is the most tested concept. Neural tube defects are prevented by periconceptional folic acid (400 mcg daily). Folinic acid (leucovorin) bypasses DHFR and is used for methotrexate rescue. Folate deficiency causes megaloblastic anaemia like B12 deficiency, but NEVER causes subacute combined degeneration (neurological damage is specific to B12 deficiency).
Clinical overview
Folic acid is an essential vitamin with critical roles in DNA synthesis, amino acid metabolism, and neural tube development. Its deficiency causes megaloblastic anaemia characterised by macrocytic red cells (MCV >100 fL) and hypersegmented neutrophils on peripheral smear. The most important clinical application of folic acid is the prevention of neural tube defects (NTDs) -- spina bifida and anencephaly -- when supplemented periconceptionally. Folic acid 400 mcg daily starting at least one month before conception and continuing through the first trimester reduces the risk of NTDs by 50-70%. In India, NTDs are a significant cause of congenital malformations, and the Government of India recommends universal folic acid supplementation for all women of reproductive age through the IFA (iron-folic acid) programme. Folic acid is also essential in the management of megaloblastic anaemia due to folate deficiency (commonly caused by poor diet, pregnancy, alcoholism, and methotrexate therapy). A critical clinical pearl is that folic acid can correct the haematological manifestations of vitamin B12 deficiency (megaloblastic anaemia) while allowing the neurological damage (subacute combined degeneration of the spinal cord) to progress irreversibly. Therefore, B12 levels must ALWAYS be checked before starting folic acid for megaloblastic anaemia. Folinic acid (leucovorin) is the reduced active form that bypasses DHFR and is used to rescue patients from methotrexate toxicity (leucovorin rescue).
Pharmacological class
Folic Acid belongs to the Water-soluble B vitamin (Vitamin B9; haematinic) class. Folic acid (pteroylglutamic acid) is the synthetic form of folate. It is reduced in the body by dihydrofolate reductase (DHFR) to tetrahydrofolate (THF), the metabolically active coenzyme. THF serves as a one-carbon carrier in numerous biosynthetic reactions: purine synthesis (de novo pathway), thymidylate synthesis (dTMP from dUMP -- essential for DNA synthesis), and the remethylation of homocysteine to methionine (requires vitamin B12 as a cofactor). Folate deficiency impairs DNA synthesis, particularly in rapidly dividing cells, causing megaloblastic anaemia.
Indian brand names and formulations
Available as: Folvite (Pfizer/Wyeth), Fol-G (Panacea Biotec), Folinal (Alkem Laboratories), IFA tablets (Government supply -- iron + folic acid).
Tablets: 5 mg (most common in India), 400 mcg (for NTD prevention). IFA tablets: ferrous sulfate 100 mg elemental iron + folic acid 500 mcg. Injection: 5 mg/mL (IM -- rarely used). Oral solution. Folinic acid (leucovorin): separate product, available as tablets and injection for methotrexate rescue.
Regulatory status
Folic Acid is classified under OTC (Over the Counter) in India under the Drugs and Cosmetics Act, 1940. Available over the counter. Part of the Anaemia Mukt Bharat programme (IFA tablets containing ferrous sulfate + folic acid). Higher doses (5 mg) are prescription-recommended for women with prior NTD pregnancies.
Indications
- Prevention of neural tube defects (periconceptional supplementation -- all women of reproductive age)
- Megaloblastic anaemia due to folate deficiency
- Pregnancy supplementation (universal recommendation)
- Methotrexate-induced folate deficiency (folic acid 5 mg weekly, given on non-methotrexate days)
- Haemolytic anaemias (increased folate turnover -- sickle cell disease, thalassaemia)
- Chronic alcoholism (dietary deficiency)
- Phenytoin-induced folate deficiency
- Homocystinuria (reduces homocysteine levels)
Dosing
NTD prevention: 400 mcg (0.4 mg) daily, starting 1 month before conception and continuing through the first trimester. High-risk women (previous NTD pregnancy, on antiepileptics): 4-5 mg daily. Megaloblastic anaemia: 5 mg daily for 4 months (then reassess). Maintenance: 5 mg once weekly. Methotrexate co-therapy: 5 mg once weekly (not on the same day as methotrexate). Pregnancy (routine): 500 mcg daily (as part of IFA supplementation per Government of India). Children: 100-500 mcg daily depending on age.
Contraindications
- Undiagnosed megaloblastic anaemia (MUST rule out B12 deficiency first)
- Pernicious anaemia treated with folic acid alone (will correct anaemia but allow irreversible subacute combined degeneration)
- Folate-dependent malignancies (theoretical concern -- folic acid may promote tumour growth, though clinical evidence is equivocal)
Adverse effects
- Generally very safe with minimal side effects
- Rare allergic reactions (rash, pruritus, bronchospasm)
- GI disturbance at very high doses (nausea, bloating)
- Masking of B12 deficiency (MOST IMPORTANT clinical concern -- corrects haematological picture while neurological damage progresses)
- Seizure risk in patients on antiepileptics (high-dose folic acid may reduce antiepileptic drug levels)
Drug interactions
- Methotrexate -- folic acid antagonises the antifolate effect of methotrexate (this is both the basis of leucovorin rescue and a reason to separate dosing days)
- Phenytoin, carbamazepine, phenobarbital -- anticonvulsants increase folate metabolism; conversely, folic acid may reduce anticonvulsant drug levels
- Trimethoprim, pyrimethamine -- DHFR inhibitors that impair folate activation
- Sulfasalazine -- reduces folate absorption
- Oral contraceptives -- may reduce serum folate levels
Pregnancy and lactation
Category A. Folic acid supplementation is the single most important pharmacological intervention for preventing neural tube defects. The WHO, ACOG, FOGSI, and Government of India all recommend universal periconceptional folic acid supplementation. Since many pregnancies are unplanned, folic acid supplementation is recommended for ALL women of reproductive age. Folic acid is safe at recommended doses throughout pregnancy.
Exam-style clinical scenario
A 65-year-old vegetarian woman presents with anaemia (Hb 7 g/dL), MCV 115 fL, and hypersegmented neutrophils on peripheral smear. She also has numbness and tingling in both feet and difficulty walking (ataxia). A well-meaning junior doctor starts folic acid 5 mg daily. After 2 weeks, her Hb improves to 9 g/dL but her neurological symptoms have worsened. What went wrong? Answer: This patient has vitamin B12 deficiency (vegan diet + megaloblastic anaemia + subacute combined degeneration). Folic acid corrected the haematological manifestation (anaemia) by providing an alternative substrate for DNA synthesis, but it cannot treat the neurological damage caused by B12 deficiency (demyelination of dorsal columns and lateral corticospinal tracts). By correcting the anaemia, folic acid masked the diagnosis of B12 deficiency, allowing irreversible neurological damage to progress. Rule: ALWAYS check B12 before treating megaloblastic anaemia with folic acid alone.
Cost in India
INR 5-15 per strip of 30 tablets (5 mg); IFA tablets: FREE through government supply
Clinical governance
Author: MedNext Editorial Team. Clinical reviewer: Awaiting clinical review. Jurisdiction: India (Drugs and Cosmetics Act, 1940). Sources: CIMS India, Indian Pharmacopoeia. Publication state: Awaiting clinical review. Correction: Report errors at support@mednext.academy.
Frequently Asked Questions
How does folic acid mask B12 deficiency?
Vitamin B12 is required to convert methyltetrahydrofolate (methyl-THF) back to THF (the active coenzyme form). In B12 deficiency, folate is trapped as methyl-THF (the 'methyl-folate trap'), causing functional folate deficiency and megaloblastic anaemia. Supplementing folic acid bypasses this trap by providing excess substrate for conversion to THF, correcting the anaemia. However, B12 is independently required for the methylmalonyl-CoA mutase reaction in myelin synthesis. Folic acid cannot substitute for this function, so neurological damage continues unchecked while the normalised blood count falsely reassures the clinician.
Why is folic acid critical in the first trimester specifically?
Neural tube closure occurs between days 21-28 after conception (often before a woman knows she is pregnant). Folic acid is essential for the rapid cell division and DNA synthesis required during neural tube closure. Deficiency during this critical window results in failure of neural tube closure, causing anencephaly (failure of cranial closure) or spina bifida (failure of caudal closure). This is why supplementation must begin BEFORE conception and continue through the first trimester.
What is the difference between folic acid and folinic acid (leucovorin)?
Folic acid is the synthetic oxidised form that must be reduced by DHFR to become active (THF). Folinic acid (leucovorin, 5-formyl-THF) is already a reduced and active folate coenzyme that does NOT require DHFR for activation. This distinction is critical in methotrexate therapy: methotrexate inhibits DHFR, so folic acid cannot be converted to THF in the presence of methotrexate. Leucovorin bypasses the DHFR block and directly provides active THF to rescue normal cells from methotrexate toxicity (leucovorin rescue), while cancer cells with higher metabolic demand are still affected.
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