cyanocobalamin

Vitamins. Haemopoietic stimulants

ATC code: B03BA01 (Cyanocobalamin)

Brand names – drugs

Cyanokit

Brand names – supplements

Solgar Sublingual Methylcobalamin, Jarrow Formulas Methyl B-12, Thorne Methylcobalamin

Supplements are not tested in clinical trials and are not registered as medications.

Mechanism of action

Cyanocobalamin (vitamin B12) is a cofactor for two enzymes: methionine synthase (remethylation of homocysteine to methionine) and methylmalonyl-CoA mutase (branched-chain fatty acid metabolism). It is required for DNA synthesis, myelination of nerve fibres, and erythrocyte maturation. Deficiency impairs erythrocyte precursor division (megaloblastic haematopoiesis) and causes demyelination of the posterior and lateral spinal cord columns.

Indications

B12 deficiency with neurological symptoms

First line

In subacute combined degeneration and other neurological features of B12 deficiency, high-dose parenteral cyanocobalamin or hydroxocobalamin is the only disease-modifying therapy. Maximal recovery occurs in the first 6 months, before irreversible axonal degeneration develops. With late treatment, neurological deficit may partially persist. Early suspicion of B12 deficiency prompts B12 and homocysteine testing without delaying therapy until results return.

Practical notes

Timing and administration

Oral forms are taken regardless of meals. Sublingual forms are placed under the tongue until dissolved – additional benefit over swallowing in people with low gastric acidity or atrophic gastritis is not proven, as intestinal absorption at high doses is comparable.

Dose titration

Deficiency treatment: 1,000–2,000 µg daily orally or 1,000 µg intramuscularly on schedule (pernicious anaemia). Prophylaxis in vegans and metformin users: 500–1,000 µg daily 1–2 times weekly or 250 µg daily. Physiological adult daily requirement is 2.4 µg – hundreds of times less than therapeutic doses because oral absorption is low (1–2% without intrinsic factor).

Monitoring

4–8 weeks after starting therapy, check complete blood count (haemoglobin, MCV) and serum B12. Haemoglobin normalises over 4–8 weeks, MCV over up to 3 months. Neurological symptoms improve more slowly – over 6–12 months. Homocysteine and methylmalonic acid are more sensitive deficiency markers, used in unclear cases.

Special situations

Patients on metformin for more than 4 years, with atrophic gastritis, after gastrectomy or ileal resection, with chronic pancreatitis, or with small intestinal bacterial overgrowth are at high risk. Vegans without supplementation inevitably develop deficiency within 3–5 years. In adults over 65, deficiency prevalence reaches 20%.

Common myths

Myth: “B12 injections give energy”. Fact: in patients with normal B12, there is no effect on energy or performance. Popular vitamin cocktails and B12 drips for healthy people lack evidence and carry injection-related risks.

Myth: “methylcobalamin is better than cyanocobalamin”. Fact: both forms are effective for deficiency correction. Methylcobalamin is more expensive, and direct RCTs showing superiority are absent. Cyanocobalamin converts to active coenzyme forms in the body.

Myth: “oral treatment doesn't work in pernicious anaemia”. Fact: the 2018 Cochrane review showed comparable efficacy of high-dose oral and parenteral routes. In neurological involvement and severe anaemia, injections are preferred in the first 2–4 weeks, then switching to tablets is possible.

Frequently asked

What is cyanocobalamin used for?

cyanocobalamin is evaluated for the following indications with varying evidence strength: Vitamin B12 deficiency anaemia (pernicious anaemia) (evidence tier A), B12 deficiency with neurological symptoms (evidence tier A), Chronic fatigue (evidence tier F). See the full indication matrix with dosing and citations above on this page.

What are the side effects of cyanocobalamin?

Common side effects of cyanocobalamin (≥ 1 in 100): Injection site pain, Allergic reactions (urticaria, pruritus). See the Safety section for uncommon and serious reactions.

Is cyanocobalamin safe during pregnancy?

FDA category A. Safe at recommended doses. Pregnant vegans and women with confirmed deficiency require supplementation – maternal B12 deficiency increases the risk of neural tube defects and developmental delay in the foetus.

Is cyanocobalamin compatible with breastfeeding?

Transfers into breast milk. Maternal B12 deficiency (especially in vegan mothers) causes infant deficiency during breastfeeding – maternal supplementation is required.

Who should not take cyanocobalamin?

cyanocobalamin is contraindicated in: Hypersensitivity to cyanocobalamin or other components; Polycythaemia vera, erythrocytosis; Thromboembolic disease (relative). Full list in the Safety section.

“B12 injections give energy”

in patients with normal B12, there is no effect on energy or performance. Popular vitamin cocktails and B12 drips for healthy people lack evidence and carry injection-related risks.

“methylcobalamin is better than cyanocobalamin”

both forms are effective for deficiency correction. Methylcobalamin is more expensive, and direct RCTs showing superiority are absent. Cyanocobalamin converts to active coenzyme forms in the body.

“oral treatment doesn't work in pernicious anaemia”

the 2018 Cochrane review showed comparable efficacy of high-dose oral and parenteral routes. In neurological involvement and severe anaemia, injections are preferred in the first 2–4 weeks, then switching to tablets is possible.

cyanocobalamin

Mechanism of action

Indications

B12 deficiency with neurological symptoms

Vitamin B12 deficiency anaemia (pernicious anaemia)

Chronic fatigue

Practical notes

Timing and administration

Dose titration

Monitoring

Special situations

Common myths

Drug–nutrient interactions

Folate

Safety

Contraindications

Serious adverse effects

Common adverse effects

Uncommon adverse effects

PregnancyFDA A

Breastfeeding

Frequently asked