< LEADERBOARD/s/vitamin-b12Vitamins

Vitamin B12

Also sold as: Cobalamin · Cyanocobalamin · Methylcobalamin

An essential vitamin for blood formation, neurological function and one-carbon metabolism. Correcting deficiency matters; an energy or memory boost in people with adequate status is not established.

Focus Energy

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Research

FocusLimited · no benefit EnergyNo established evidence

Focus: A 16-RCT synthesis with 6276 participants found no cognitive-domain benefit in people without overt deficiency or advanced neurological disease.
Energy: Fatigue benefit outside deficiency is unestablished; only one fatigue study was available in the cited synthesis, too little for pooling.

REALITY CHECK // Correcting B12 deficiency is different from boosting an already adequate person. The largest supplied cognitive synthesis was negative and the fatigue evidence was too sparse for a reliable estimate. Methylcobalamin has no established clinical superiority over cyanocobalamin here, while high blood B12 and cancer associations do not by themselves prove supplement causation.

Levels: how we grade evidence. Grey = evidence of no benefit; amber = evidence it makes this goal worse.

Ratings are self-reported by a self-selected group of users: how it felt, not proof that it works.

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Check your bottle

Compare what your label says with what was used in trials. This is a trial range, not a personal prescription.

Enter the amount from your label to see the result.

How it was studied

01 // STUDIED_DOSE_RANGE

1000-2000 micrograms orally

Stored as 1-2 mg in this calculator. These deficiency-treatment trial amounts are not a routine wellness target.

02 // TIMING_&_MATRIX

Route is a clinical choice

High oral doses can use passive absorption; sublingual administration is not proven universally superior. Do not apply oral ranges to injections.

03 // EVALUATION_WINDOW

Deficiency treatment needs follow-up

Interpret symptoms, blood counts and relevant tests clinically. No immediate nondeficient energy boost is established.

04 // SAFETY_&_QUALITY_GATE

No established UL

Check cobalt allergy, neurological symptoms, dietary risk and medicines. More is not automatically better.

UPPER LIMIT // No tolerable upper intake level is established by EFSA or NIH in the supplied dossier. This reflects low documented toxicity, not demonstrated benefit or unlimited safety at escalating doses. Numeric UL fields therefore remain null.

NERD'S NOTENerd Protocols · a clinical and sports dietitian based in the EU

Summary

B12 is useful for correcting deficiency, not as a general stimulant. Oral 1000-2000 micrograms/day raised B12 and improved deficiency-related laboratory findings comparably to intramuscular treatment in small studies; evidence quality and clinical-outcome reporting are limited. A 16-RCT synthesis found no cognitive benefit without overt deficiency, and fatigue evidence was too sparse to establish benefit.

Mechanism

Cobalamin supports methionine synthase and methylmalonyl-CoA mutase, linking it to one-carbon metabolism, blood formation and nerve function. A small fraction of a large oral dose is passively absorbed independently of intrinsic factor. More efficient methylation as a marketing phrase does not establish better cognition or mood in a replete person.

Typical studied dose

Deficiency trials used approximately 1000-2000 micrograms/day orally, equal to 1-2 mg/day. These are treatment-study amounts, not universal preventive doses. No optimal dose for otherwise replete people is established. Injections and urgent neurological presentations require a clinician-directed regimen rather than extrapolation from an oral calculator.

Upper limit

No tolerable upper intake level is established by EFSA or NIH in the supplied dossier. This reflects low documented toxicity, not demonstrated benefit or unlimited safety at escalating doses. Numeric UL fields therefore remain null.

POPULAR_STACKScombos with n ≥ 5

Popular stacks with Vitamin B12

Not enough stack data yet. A combination with Vitamin B12 appears here once 5 people rate the same set.

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Forms and label traps

Forms compared
Form on label	Active content	Studied range / day	Absorption & GI tolerance	Verdict
Oral cyanocobalamin Best for: Comparison with high-dose oral deficiency research.	Extract weight · ~100% marker	1–2 mg	Stable, well studied and inexpensive; a small fraction of large doses is passively absorbed. Generally well tolerated.	Studied standard [DOSSIER // REFERENCE] 1 mg equals 1000 micrograms. This 100% identifies declared vitamin mass, not the absorbed fraction; no 1% bioavailability multiplier is used. PMID 29543316
Methylcobalamin Best for: People examining active-form or methylation claims.	Unstandardized: active content unknown	no comparable trial range	Coenzyme form; strong head-to-head clinical superiority over cyano is not established. Generally tolerated; agitation reports are anecdotal.	Good option [DOSSIER // CHECK_FORM] No distinct form-specific trial interval supplied. Do not infer benefit from MTHFR marketing or apply cyano-trial ranges automatically.
Hydroxocobalamin, especially injection products Best for: Clinician-led deficiency treatment where this route is chosen.	Unstandardized: active content unknown	no comparable trial range	Longer retention is described in the dossier; cellular uptake comparisons are laboratory evidence. Injection-route effects require clinician assessment.	Caution [DOSSIER // CHECK_FORM] No oral-to-injection mg equivalence or treatment schedule is calculated. PMID 38337663
Adenosylcobalamin or dibencozide Best for: Understanding blended active-form labels.	Unstandardized: active content unknown	no comparable trial range	Mitochondrial coenzyme form; sparse direct clinical comparisons. Generally tolerated in the source dossier.	Good option [DOSSIER // CHECK_FORM] No demonstrated superiority or form-specific trial target is supplied.

Common label traps

TRAP_01 // B12 GIVES ENERGY EVEN WITHOUT DEFICIENCY
Fatigue benefit is not established in replete people; the supplied synthesis had only one fatigue study.
TRAP_02 // METHYLATED MEANS CLINICALLY SUPERIOR
Active-form biochemistry does not replace head-to-head clinical outcome evidence.
TRAP_03 // CYANO MEANS A TOXIC CYANIDE DOSE
The source describes the cyanide amount in usual B12 products as clinically minor; this does not override individual contraindications.
TRAP_04 // EVERYONE NEEDS INJECTIONS
High-dose oral therapy can correct many deficiencies. Severe symptoms or particular clinical contexts still require individualized route selection.
TRAP_05 // LOWER HOMOCYSTEINE GUARANTEES HEART OR BRAIN PROTECTION
The biomarker falls more reliably than clinical cardiovascular or cognitive outcomes improve.

Other outcomes studied

Outside the five leaderboard goals. Same evidence levels as above.

DEFICIENCY CORRECTION Moderate · benefit
Small oral-versus-injection trials support serum B12 correction with oral 1-2 mg/day. Clinical neurological and hematological outcome reporting is limited; route and urgency remain clinical decisions.
PMID 29543316 PMID 41487531 PMID 16034940
DEPRESSION WITHOUT DEFICIENCY Limited · no benefit
No clear short-term benefit for depressive episodes. Possible longer-term relapse-prevention findings are weak; dietary associations do not prove causation.
PMID 25644193 PMID 33809274 PMID 33912967
DIABETIC OR METFORMIN-RELATED NEUROPATHY Limited · benefit
Correcting deficiency is justified when present. Neuropathy findings outside deficiency are mixed and low certainty; observational low-B12 associations are not causal proof.
PMID 36240684 PMID 28081987
HOMOCYSTEINE AND VASCULAR OUTCOMES Limited · no benefit
B-vitamin combinations reduce homocysteine more consistently than they improve clinical outcomes. MI/CV mortality benefit is unestablished, and any stroke signal may depend on folate and population.
PMID 20413740
COGNITIVE OUTCOMES AFTER STROKE OR TIA Limited · no benefit
Combination B-vitamin studies do not establish that reducing homocysteine prevents cognitive impairment or that B12 alone provides a benefit.
PMID 23765945 PMID 22232016
HIGH B12 AND CANCER ASSOCIATIONS Limited · makes it worse
Observational high-serum-B12 and high-dose B6+B12 signals require caution about confounding and reverse causality; they do not establish that B12 supplements cause cancer.

Reader questions

Can I just take more because excess is excreted?

No established UL does not mean an escalating dose has a benefit. Match use to dietary risk or a clinical indication and investigate unexplained symptoms or high test results.

Is methylcobalamin better than cyanocobalamin?

The dossier lacks robust human outcome evidence proving superiority. A coenzyme label or MTHFR genotype claim alone is not that evidence.

Tablets, sublingual products or injections?

High-dose oral therapy works for many deficiencies; sublingual administration has not shown universal superiority. Severe symptoms and route selection need a clinician.

Does B12 cause lung cancer?

The signal described here comes from observational high-dose B6+B12 studies, not proof of causation. High serum B12 may also reflect disease rather than supplement toxicity; discuss your context without interpreting an association as a diagnosis.

Why do I feel anxious after methylated B12?

Agitation and panic-like reports are anecdotal; the dossier has no controlled mechanism or incidence estimate. Review persistent symptoms and the full product rather than assuming a methylation disorder.

Stack interactions

Caution Metformin [CAUTION // REVIEW_WITH_CLINICIAN]
Long-term treatment can lower B12; deficiency and neuropathy context merit monitoring. A systematic review addresses supplementation in metformin-treated diabetes, not a universal energy stack.
PMID 36240684
Caution High-dose folate [CAUTION // REVIEW_WITH_CLINICIAN]
Folate may improve the anemia while B12-related neurological injury progresses. Assess B12 before prolonged high-dose folate; this precaution lacks an individually indexed supporting reference here.
Caution Proton-pump inhibitors and H2 blockers [CAUTION // REVIEW_WITH_CLINICIAN]
Reduced release of food-bound B12 is a dossier precaution; source-paper verification remains outstanding.
Danger Nitrous oxide [CAUTION // REVIEW_WITH_CLINICIAN]
Cobalamin inactivation is flagged in the source. Repeated exposure with neurological symptoms requires medical assessment; no paper-specific citation is supplied here.
Caution Chloramphenicol, colchicine and high-dose vitamin C [CAUTION // REVIEW_WITH_CLINICIAN]
The dossier flags possible hematological response/absorption effects for the medicines. The vitamin C claim is weak laboratory-based evidence; no established clinical degradation effect or mandatory spacing rule is inferred.

Red flags: interactions and who should avoid it

Interactions

Long-term metformin use can lower B12 status; monitoring and correction may be relevant. Acid-suppressing drugs can impair release of food-bound B12; this dossier lacks a paper-specific interaction reference. High-dose folate may correct anemia while B12-related neurological injury continues. Nitrous oxide can inactivate cobalamin; that precaution is present but individually unsourced here. Chloramphenicol and colchicine precautions also need paper-level verification.

Avoid or ask a doctor first if

Known cobalt or cobalamin hypersensitivity requires medical review. The dossier flags cyanocobalamin in Leber hereditary optic neuropathy; specialist guidance is required. Severe renal disease and unusual neurological symptoms warrant assessment rather than self-treatment. Pregnancy and breastfeeding are not blanket contraindications: adequate B12 is important, particularly with vegan diets. Unexplained high serum B12 can reflect underlying disease and deserves interpretation rather than reflexive dose escalation.

Sources (PubMed, 12)

Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency.
PMID 29543316 · 2018 · systematic review and meta-analysis
Oral versus intramuscular deficiency treatment: small studies and limited clinical-outcome certainty.
Efficacy of sublingual and oral vitamin B12 versus intramuscular administration: insights from a systematic review and meta-analysis.
PMID 41487531 · 2025 · systematic review and meta-analysis
Route-comparison synthesis including oral, sublingual and intramuscular administration.
Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency.
PMID 16034940 · 2005 · systematic review and meta-analysis
Earlier oral versus injection deficiency-treatment evidence.
Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression.
PMID 33809274 · 2021 · systematic review and meta-analysis
No cognitive benefit without overt deficiency and insufficient fatigue trials for pooling.
Effect of homocysteine lowering treatment on cognitive function: a systematic review and meta-analysis of randomized controlled trials.
PMID 22232016 · 2012 · systematic review and meta-analysis
Homocysteine lowering does not establish improved cognitive function.
Systematic review and meta-analysis of randomized placebo-controlled trials of folate and vitamin B12 for depression.
PMID 25644193 · 2015 · systematic review and meta-analysis
No clear short-term depressive-episode benefit; weak longer-term prevention signals.
Associations of dietary vitamin B1, vitamin B2, vitamin B6, and vitamin B12 with the risk of depression: a systematic review and meta-analysis.
PMID 33912967 · 2022 · systematic review and meta-analysis
Dietary B-vitamin and depression associations, explicitly observational.
The efficacy of vitamin B12 supplementation for treating vitamin B12 deficiency and peripheral neuropathy in metformin-treated type 2 diabetes mellitus patients: A systematic review.
PMID 36240684 · 2022 · systematic review and meta-analysis
B12 deficiency and neuropathy treatment context in metformin-treated diabetes.
Serum folate, vitamin B12 levels and diabetic peripheral neuropathy in type 2 diabetes: A meta-analysis.
PMID 28081987 · 2017 · systematic review and meta-analysis
Observational folate/B12 levels and diabetic-neuropathy associations.
Efficacy of homocysteine-lowering therapy with folic Acid in stroke prevention: a meta-analysis.
PMID 20413740 · 2010 · systematic review and meta-analysis
Folic-acid-containing homocysteine-lowering stroke research; cannot attribute effects to B12 alone.
Effect of B vitamins and lowering homocysteine on cognitive impairment in patients with previous stroke or transient ischemic attack: a prespecified secondary analysis of a randomized, placebo-controlled trial and meta-analysis.
PMID 23765945 · 2013 · systematic review and meta-analysis
Combination B vitamins and cognitive outcomes after stroke/TIA.
Kinetics of Cellular Cobalamin Uptake and Conversion: Comparison of Aquo/Hydroxocobalamin to Cyanocobalamin.
PMID 38337663 · 2024 · laboratory study
Laboratory cellular uptake/conversion comparison; not human clinical superiority.

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