Naturally occurring vitamin B12, retained longer per injection than the common synthetic form. Strongest evidence: correcting low vitamin B12, the blood abnormalities that follow, and the marker that rises when the vitamin is lacking. Heart and brain outcomes remain unproven. Harms follow dose: benign at replacement doses, kidney and blood pressure concerns at emergency doses. (Full Review)

Protocol

Standard European loading regimen

1 mg intramuscularly, three times weekly for two weeks

Or on alternate days for 5–6 doses; for correcting established deficiency

Maintenance after loading

1 mg intramuscularly every 2–3 months

Tightened to every two months where neurological signs were present

Competing approach — oral high-dose

1,000–2,000 µg daily oral or sublingual

Passive diffusion needs no intrinsic factor; comparable serum normalisation at lower cost

Time to effect

Blood counts

6–8 weeks

Reticulocyte counts rise within 3–7 days

Homocysteine

12 weeks or more

Larger reductions with doses above 500 µg daily

Nerve symptoms

3–6 months

May not fully resolve if deficiency lasted more than a year

Benefits

High: Correction of vitamin B12 deficiency and its blood abnormalities; lowering of homocysteine

Medium: Prevention of vasoplegic syndrome after cardiac surgery

Low: Reduction of low back pain in combination therapy; longer retention per dose than cyanocobalamin; survival after cyanide exposure from smoke inhalation (conflicted); neurological recovery after nitrous oxide misuse

Speculative: Attenuation of cellular ageing processes

Contraindications

Documented anaphylaxis or immediate hypersensitivity to any cobalamin or to cobalt

Untreated polycythaemia vera or another myeloproliferative disorder, until controlled

Gram-scale intravenous dosing only: primary hyperoxaluria, recurrent calcium-oxalate stones, chronic kidney disease with eGFR below 30 mL/min/1.73 m²

Gram-scale intravenous dosing only: uncontrolled hypertension above 160/100 mmHg

Key Interactions

Nitrous oxide (anaesthetic and recreational): absolute avoidance during cobalamin depletion

Metformin: caution and monitoring

Proton pump inhibitors and H2 blockers (omeprazole, esomeprazole, famotidine): caution

Colchicine and aminosalicylic acid: caution

Chloramphenicol: caution

High-dose vitamin C supplements: caution

Folic acid supplements: caution

Supplements with additive homocysteine-lowering effects: folate, vitamin B6, riboflavin, betaine, creatine

Potassium-lowering agents (hydrochlorothiazide, furosemide, indapamide): caution during the first week of treating severe anaemia

Haemodialysis and blood-leak detectors: caution

Risk & Side Effects

High: Chromaturia and red discoloration of skin and mucous membranes; rise in blood pressure

Medium: Acute kidney injury and oxalate nephropathy; invalidation of laboratory and blood-gas results

Low: Hypersensitivity and anaphylaxis; acneiform eruptions; hypokalaemia during rapid correction of severe deficiency; elevated circulating B12 as an outcome marker (conflicted)

Speculative: Methaemoglobinaemia

Monitoring

Marker	Target	Why
Serum vitamin B12 (total)	500–900 pg/mL	Screening measure of total circulating cobalamin
Holotranscobalamin	Above 50 pmol/L	The fraction actually deliverable to cells
Methylmalonic acid (MMA)	Below 0.27 µmol/L	Rises when cobalamin is functionally lacking inside cells
Homocysteine	5–8 µmol/L	Confirms functional cobalamin sufficiency and tracks vascular risk
Mean corpuscular volume (MCV)	82–90 fL	Enlarged red cells signal impaired DNA synthesis
Serum folate	10–20 ng/mL	Distinguishes folate deficiency, which mimics cobalamin deficiency
Ferritin	50–150 ng/mL	Iron shortage prevents blood counts correcting despite repletion
Potassium	4.0–4.5 mmol/L	Falls as new red cells are produced during rapid correction
Estimated glomerular filtration rate (eGFR)	Above 90 mL/min/1.73 m²	Governs oxalate handling and the interpretation of MMA
Intrinsic factor antibodies	Negative	Identifies pernicious anaemia, which makes treatment lifelong

Cadence: Baseline panel before the first dose; potassium and complete blood count at 1 week during loading; methylmalonic acid, homocysteine and complete blood count at 8 weeks; full panel every 6–12 months on maintenance

Qualitative Assessment

Energy through the afternoon rather than only on waking
Tingling, numbness or burning in the hands and feet
Balance and gait steadiness, particularly in the dark
Word-finding, short-term recall and mental clarity
Mood stability, irritability and motivation
Tongue soreness or smoothness, and mouth ulceration
Sleep depth and ease of falling asleep after dose changes

Hydroxocobalamin for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment