Vitamin B12 (Cyanocobalamin / Methylcobalamin)
Also sold as: Neurobion, Mecobalamin, Cobamin, Methycobal, Nervup, Cobaday, Nucoxan, Methycobal OD
Pregnancy
Cat A
Lactation
Safe
Schedule
OTC
Forms
Tablet cyanocobalamin 500 mcg +6
Indications
- Vitamin B12 deficiency (serum B12 <200 pg/mL)
- Pernicious anaemia (autoimmune gastritis with intrinsic factor deficiency — requires IM B12)
- Megaloblastic anaemia from B12 deficiency
- B12 deficiency neuropathy (subacute combined degeneration of spinal cord)
- Vegan / Vegetarian diet–related B12 deficiency
- Metformin-induced B12 depletion (metformin blocks B12 absorption)
- PPI-induced B12 deficiency (long-term PPI use reduces gastric acid needed for B12 release)
- Post-gastrectomy / Ileal resection B12 malabsorption
- Diabetic peripheral neuropathy (methylcobalamin — adjunct; evidence for neuroprotection)
- B12 deficiency in elderly (achlorhydria common in elderly)
Adult Dosing
B12 deficiency without neurological involvement
Oral: 1000–2000 mcg daily for 4 weeks; then 1000 mcg daily maintenance. IM: 1000 mcg daily × 7 days, then weekly × 4 weeks, then monthly maintenance.
Pernicious anaemia or malabsorption: lifelong IM injection monthly
High-dose oral B12 can achieve adequate absorption even without intrinsic factor via passive diffusion (approximately 1% of dose); effective alternative to IM in many cases except severe malabsorption.
B12 deficiency with neurological involvement
IM: 1000 mcg daily for 7 days, then every other day for 3 weeks, then every 3 days for 3 weeks, then monthly — or per neurologist guidance
Aggressive initial replacement; neurological response may take months
Neurological damage can be permanent if not treated promptly; DO NOT delay treatment if clinical features present
Pernicious anaemia — lifelong maintenance
IM cyanocobalamin 1000 mcg every month (lifelong)
Lifelong — intrinsic factor deficiency means oral B12 poorly absorbed without supplementation
Dietary deficiency / Prevention (vegans)
500–1000 mcg daily oral (cyanocobalamin or methylcobalamin)
Daily; ongoing while on vegan/vegetarian diet
Metformin-induced B12 depletion
500–1000 mcg daily oral
Long-term with metformin therapy; annual B12 monitoring
ADA recommends annual B12 monitoring in all metformin users; check at baseline when starting metformin
Diabetic neuropathy (adjunct; methylcobalamin)
Methylcobalamin 500 mcg three times daily or 1500 mcg once daily
3–6 months; evidence supports neuroprotective role; not substitutes for glucose control
Pediatric Dosing
B12 deficiency in breastfed infants of vegan mothers can cause severe, irreversible neurological damage. Mothers must supplement; infants of vegan mothers should receive B12 drops. Treatment doses: 1000 mcg IM initially for severe deficiency.
Renal Dose Adjustment
| CrCl / eGFR | Dose Adjustment |
|---|---|
| Any CKD stage | No dose adjustment required; B12 is water-soluble and safe in renal impairment |
Hepatic Adjustment
No dose adjustment required. Vitamin B12 stored extensively in liver — liver disease may release B12 from stores causing misleadingly elevated serum B12 levels despite functional deficiency.
Pregnancy & Lactation
Pregnancy: Category A
Vitamin B12 is essential for fetal neural development. B12 deficiency in pregnancy causes increased risk of neural tube defects (synergistic with folate), fetal growth restriction, and preterm birth. Supplementation is safe and recommended — all prenatal vitamins should contain adequate B12. Vegan pregnant women require careful monitoring and supplementation.
Lactation: Safe
B12 is safe and essential during breastfeeding. Breast milk B12 content depends on maternal status — deficient mothers produce B12-deficient milk causing severe infant neurological damage. Vegan/vegetarian breastfeeding women MUST supplement B12.
Top Drug Interactions
| Interacting Drug | Effect | Severity |
|---|---|---|
| Metformin | Metformin reduces B12 absorption by interfering with calcium-dependent ileal absorption of the B12-intrinsic factor complex; progressive B12 depletion occurs in 10–30% of metformin users; monitor annually | Moderate |
| Proton pump inhibitors (omeprazole, pantoprazole) | Reduced gastric acid production impairs B12 release from food protein; long-term PPI use increases B12 deficiency risk; monitor B12 annually in long-term PPI users | Moderate |
| H2-blockers (ranitidine, famotidine) | Similar mechanism to PPIs — reduced acid impairs food-bound B12 absorption; less impact than PPIs | Minor |
| Chloramphenicol | Chloramphenicol interferes with haematopoietic response to B12; monitor during concurrent use | Moderate |
| Colchicine / Aminosalicylic acid (PAS) | Reduce B12 absorption from the ileum; monitor B12 in patients on these agents long-term | Minor |
| Folic acid (high dose) | High-dose folic acid can correct megaloblastic anaemia from B12 deficiency while masking the deficiency and allowing irreversible neurological damage to progress; always check B12 status when prescribing high-dose folic acid | Major |
DoctorScribe — AI Medical Scribe
Stop looking up Vitamin B12 — just speak the prescription
"Vitamin B12 as per dose, BD for 5 days." DoctorScribe writes the full prescription with brand, strength, frequency, and route — auto-applies pediatric weight-based dosing and renal adjustments. Try the live demo.
Side Effects
Common
- Generally very well tolerated — no significant side effects at standard doses
- Injection site pain (IM cyanocobalamin injections)
- Mild diarrhea (rare)
- Nausea (rare)
- Rash / Acne (rare reports with cyanocobalamin; methylcobalamin preferred if this occurs)
- Urine may appear bright yellow (harmless — riboflavin component in B complex formulations)
Serious / Discontinue If
- Anaphylaxis to cyanocobalamin injection (rare; benzyl alcohol preservative may be implicated)
- Hypokalemia — during initial intensive therapy of severe megaloblastic anaemia, potassium rapidly taken up by new red cells during haematopoietic response; monitor potassium during aggressive B12 replacement
- Peripheral vascular thrombosis (rare, with rapid high-dose therapy — theoretical)
- Masking of polycythaemia vera (correction of B12 deficiency anaemia may reveal underlying polycythaemia)
Contraindications
- Hypersensitivity to cyanocobalamin, cobalamin, or cobalt
- Leber's hereditary optic neuropathy (cyanocobalamin CONTRAINDICATED — worsens condition; use hydroxocobalamin instead)
- Tobacco amblyopia (cyanocobalamin contraindicated; use hydroxocobalamin)
Available Indian Brands
| Brand | Manufacturer | Price (approx) |
|---|---|---|
| Neurobion | MSD India (B1 + B6 + B12 combination) | 30 tab ₹85 |
| Mecobalamin | Mankind Pharma (methylcobalamin 500 mcg) | 10 tab ₹38 |
| Methycobal | Eisai Pharmaceuticals India (methylcobalamin 500 mcg) | 10 tab ₹62 |
| Cobamin | Lupin Ltd (cyanocobalamin 1000 mcg IM) | 5 amp ₹45 |
| Nervup OD | Sun Pharmaceutical (methylcobalamin 1500 mcg) | 10 tab ₹55 |
| Nucoxan | Abbott India (methylcobalamin 500 mcg) | 10 tab ₹58 |
| Cobaday | Alkem Laboratories (methylcobalamin 1500 mcg) | 10 tab ₹50 |
Monitoring Required
- Serum vitamin B12 level (baseline; repeat at 3 months after supplementation start; target >300 pg/mL)
- Complete blood count (CBC) — Hb, MCV, MCH (megaloblastic changes); reticulocyte count (rises within 5–7 days of treatment)
- Serum homocysteine and/or methylmalonic acid (MMA) — more sensitive markers of functional B12 deficiency; useful when serum B12 borderline 200–300 pg/mL
- Serum folate (concurrent deficiency common; treat both)
- Serum potassium (during initial aggressive therapy of severe megaloblastic anaemia)
- Peripheral blood smear (hypersegmented neutrophils — early megaloblastic change)
- Neurological assessment (symptoms: tingling, numbness, gait abnormalities, cognitive decline)
- Annual B12 monitoring in: all metformin users, long-term PPI users, vegans, elderly >65 years, post-gastric surgery
Patient Counseling Points
- If you are vegetarian or vegan, you are at high risk of vitamin B12 deficiency — B12 is found almost exclusively in animal foods (meat, fish, eggs, dairy); supplement daily
- If you are on metformin (for diabetes), get your vitamin B12 level checked every year — metformin reduces B12 absorption
- If you are on long-term acid-reducing tablets (omeprazole, pantoprazole), get B12 checked annually
- B12 deficiency causes nerve damage that can be PERMANENT if not treated promptly — do not delay if experiencing tingling, numbness, or balance problems
- For pernicious anaemia (intrinsic factor deficiency): you will need monthly B12 injections for LIFE; oral B12 alone is not sufficient
- High-dose oral B12 (1000–2000 mcg/day) can be effective even without intrinsic factor via passive absorption — discuss with your doctor
- Methylcobalamin is the active, biologically usable form of B12; cyanocobalamin must be converted in the body
- B12 is water-soluble and extremely safe — excess is excreted in urine; no risk of toxicity from high doses
- Folic acid alone will NOT treat B12 deficiency neuropathy — B12 must be replaced separately
Stop Googling drug references mid-consultation
EasyClinic auto-flags Vitamin B12 interactions, renal cutoffs, and pregnancy warnings the moment you write the prescription. Built-in safety net for every Indian doctor.
Clinically reviewed by: Dr. Vijay Sheth, MD (Medicine), DM (Haematology), Bombay Hospital and Medical Research Centre Mumbai
Last reviewed: 2026-04-12
References
- ICMR — Vitamin B12 Deficiency in India — Recommendations 2021
- American Diabetes Association — Standards of Care 2024 (Metformin and B12)
- BNF 85 — Cyanocobalamin / Hydroxocobalamin
- UpToDate — Vitamin B12 deficiency: Treatment
- Indian Journal of Medical Research — Vitamin B12 deficiency in vegetarians 2020
- Prakash S et al. — Methylcobalamin in diabetic neuropathy, Indian J Neurol 2017