Vitamin B12 supplement Pregnancy: Should not be used to treat megaloblastic anaemia of pregnancy, because that anaemia is due to folate deficiency (SPC 4.6).

Cyanocobalamin

Brand names: Cytacon

Cyanocobalamin is a form of vitamin B12 used to treat and prevent vitamin B12 deficiency.

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: One to three tablets (50 to 150 micrograms) or more daily, at the discretion of the physician

Route: Oral (50 microgram tablets)

Frequency: Daily; where possible take doses between meals

Source is the UK SPC for cyanocobalamin 50 microgram ORAL tablets - parenteral (intramuscular) hydroxocobalamin/cyanocobalamin products have entirely different posology; confirm which formulation this page covers. Pernicious anaemia: intramuscular therapy is preferable for initial correction of vitamin B12 deficiency; if the oral route is used to follow this, at least 300 micrograms should be given daily. In pernicious anaemia an adequate dose must be used and the blood picture examined regularly - at least every three months for 18 months until stabilised, then annually. Indiscriminate administration may mask precise diagnosis. Elderly: the normal adult dose is appropriate. Paediatric: the SPC states one tablet (50 micrograms) daily at the discretion of the physician - a fixed dose, not weight-based. Tablets contain lactose: patients with rare hereditary galactose intolerance, total lactase deficiency or glucose-galactose malabsorption should not take this medicine.

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.

Contraindications

Hypersensitivity to the active substance or to any of the excipients

Side effects

Sensitisation is rare, but may present as an itching exanthema
Anaphylactic shock (exceptionally)
Acneiform eruptions (rare)
Bullous eruptions (rare)
Patients sensitised by injection are often able to tolerate the oral route without trouble

Interactions

Absorption may be reduced by para-aminosalicylic acid, colchicine, biguanides, neomycin, colestyramine, potassium chloride, methyldopa and cimetidine
Patients treated with chloramphenicol may respond poorly to cyanocobalamin
Oral contraceptives may lower serum vitamin B12 levels
These interactions are unlikely to have clinical significance (per the SPC)
Anti-metabolites and most antibiotics invalidate microbiological vitamin B12 assays

Clinical monograph

How it works

It is converted in the body to the active coenzymes methylcobalamin and adenosylcobalamin, which are required for DNA synthesis and normal red cell and neuronal function.

Prescribing in practice

In deficiency with neurological involvement or pernicious anaemia, parenteral hydroxocobalamin is generally preferred, as oral cyanocobalamin relies on adequate absorption.
Identify and address the underlying cause of deficiency rather than treating the blood result alone.
Correcting B12 deficiency can unmask or precipitate hypokalaemia as haematopoiesis recovers.

Monitoring

Monitor the haematological response and serum potassium during initial correction of significant deficiency.

Counselling the patient

Lifelong treatment may be needed if the cause of deficiency is permanent, such as pernicious anaemia.
Tell your team if you follow a vegan diet or have had gastrointestinal surgery, as these affect B12.
Take oral preparations as directed and report return of symptoms such as fatigue or tingling.

Evidence & guidelines

Use of vitamin B12 replacement in deficiency is long-established standard practice; consult current prescribing references on choice of preparation and route.

Reference: NICE CKS; 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.

Pathways