Hydroxocobalamin is the precursor form of vitamin B12 that the body converts to active methyl- and adenosyl-cobalamin as needed. Because the methylation step happens on-demand, it's a gentler option for people who feel overstimulated by methylcobalamin — particularly slow-COMT carriers.
Moderate evidence · Last reviewed:
Key facts
Best form
Hydroxocobalamin (oral or sublingual)
Typical dose
1000 mcg/day oral
Take with
Folate, B6
Time of day
Morning
Who tends to benefit
Slow-COMT carriers who don't tolerate methylcobalamin
People with low B12 (vegan/vegetarian diets, age 60+, PPI users)
Pernicious anemia and intrinsic-factor issues — under clinician care
MTHFR carriers seeking a balanced methyl-donor stack
How it compares to other B12 forms
Methylcobalamin — already methylated; faster active uptake but can overstimulate sensitive users
Adenosylcobalamin — supports mitochondrial energy; often paired with hydroxo for full coverage
Cyanocobalamin — cheap and stable but contains a cyanide group most people can clear; avoid in smokers and kidney disease
Dosing notes
1000 mcg/day oral or sublingual is appropriate for maintenance
Injections (typically 1 mg every 1-3 months) are used for diagnosed deficiency under clinician guidance
Re-test serum B12 + MMA (methylmalonic acid) after 8-12 weeks
Related in the knowledge graph
Biomarkers
Homocysteine — B12 repletion supports the remethylation arm of the methylation cycle and lowers homocysteine when B12 is low. Moderate evidence
Genes
COMT — Slow-COMT carriers often tolerate hydroxocobalamin better than methylcobalamin. Moderate evidence
FAQ
Is hydroxocobalamin as effective as methylcobalamin?
Yes for restoring B12 status. The body converts hydroxocobalamin to the active forms as needed, which is what makes it gentler for sensitive users.
Should I take hydroxocobalamin if I have MTHFR?
Possibly — especially if you also have a slow-COMT genotype or felt over-activated on methylcobalamin. Many MTHFR carriers do well on a stack of folinic acid + hydroxocobalamin.
References
Thakkar & Billa, Eur J Clin Nutr 2015 — PMID 25117994. Hydroxocobalamin has a longer half-life and is the preferred form for parenteral B12 replacement.