Check a pair

Vitamin B12 (Methylcobalamin)

Active form of vitamin B12 essential for nerve function, DNA synthesis, and red blood cell formation

Scientific nameMethylcobalamin FormulaC63H91CoN13O14P Molecular weight1344.38 g/mol CAS13422-55-4
85 absorption score
10 safety / 10
15 USD per month
5 documented interactions

Check it against something

Evidence level A

Vitamin B12 (Methylcobalamin) with:

Compatibility score 99 out of 100
99 out of 100
Works better together Compatible. Timing differs, so follow each supplement's own window.

Check it against your whole stack →

What it does

mechanism and evidence for each claim

Energy production support

Essential cofactor in cellular energy metabolism

Required for mitochondrial fatty acid oxidation Evidence A-grade 2-4 weeks

Neurological function

Maintains myelin sheath and nerve conduction

Essential for methylmalonyl-CoA mutase enzyme Evidence A-grade 4-12 weeks

Red blood cell formation

Prevents megaloblastic anemia

Required for DNA synthesis in rapidly dividing cells Evidence A-grade 6-8 weeks

Cognitive function

Supports memory, focus, and mental clarity

Methylation of neurotransmitters and myelin maintenance Evidence B-grade 4-8 weeks

Mood regulation

Supports synthesis of mood-regulating neurotransmitters

Methylation pathways for serotonin and dopamine Evidence B-grade 4-12 weeks

Others take these for the same thing

Same goal, different mechanism — check any of them against this one

Ashwagandha Stress management & energy 300-600mg A 75% Vitamin B12 (Cyanocobalamin) Energy & nerve support 250-1000 mcg A 70% Coenzyme Q10 (CoQ10) Heart health & cellular energy 100-200mg A 10% Fish Oil (EPA/DHA) Heart & brain health 1-2g EPA/DHA A 85% Phosphorus Bone health & energy metabolism 700-1250mg A 80% Vitamin B3 (Niacinamide) Energy & skin health (no flush) 100-1000 mg A 88%

Or a different form of the same thing

the comparison people search most
Vitamin B12 (Methylcobalamin) vs Vitamin B12 (Cyanocobalamin) absorption 85 against 70 · $15 against $8 a month 70% Vitamin B12 (Methylcobalamin) vs Vitamin B12 (Hydroxocobalamin) absorption 85 against 75 · $15 against $35 a month 75% Vitamin B12 (Methylcobalamin) vs Vitamin B12 (Adenosylcobalamin) absorption 85 against 80 · $15 against $60 a month 80%

All Vitamin B12 forms ranked by absorption →

Every pair we checked

12 combinations scored by the engine
Vitamin B12 (Methylcobalamin) + Caffeine No documented interaction either way No known interaction 70
Vitamin B12 (Methylcobalamin) + Creatine Monohydrate No documented interaction either way No known interaction 70
Vitamin B12 (Methylcobalamin) + Whey Protein No documented interaction either way No known interaction 70
Vitamin B12 (Methylcobalamin) + Turmeric No documented interaction either way No known interaction 70
Vitamin B12 (Methylcobalamin) + Lactase Improved calcium absorption when consuming dairy Works better together 82
Vitamin B12 (Methylcobalamin) + Bovine Collagen Essential for collagen synthesis and cross-linking Works better together 82
Vitamin B12 (Methylcobalamin) + DHA Prevents oxidation of DHA and enhances stability Works better together 82
Vitamin B12 (Methylcobalamin) + Betaine HCl Alternative methylation pathway support Works better together 86
Vitamin B12 (Methylcobalamin) + Vitamin D3 Both involved in homocysteine metabolism Works better together 90
Vitamin B12 (Methylcobalamin) + Fish Oil (EPA/DHA) Protects fish oil from oxidation Works better together 90
Vitamin B12 (Methylcobalamin) + Calcium Carbonate Essential for calcium absorption and utilization Works better together 94
Vitamin B12 (Methylcobalamin) + Folate (5-MTHF) Work together in methylation and DNA synthesis Works better together 99

Dosage

Morning sublingual
Daily500-1000 mcg
Maintenance250-500 mcg
Therapeutic1000-5000 mcg
MaximumNo established upper limit
ToxicNo known toxicity

Before you take it

VeganYes

When to expect it

First Effects1-2 weeks for energy improvements
Peak Benefits8-12 weeks for neurological and cognitive benefits
Deficiency Development3-5 years with no intake (due to liver stores)
Toxicity OnsetNo known toxicity at any dose

How to measure it

$60-120 for both tests
MarkerSerum B12 and MMA (methylmalonic acid)
OptimalB12: 400-900 pg/mL, MMA: <0.4 μmol/L
Deficient belowB12: <200 pg/mL, MMA: >0.4 μmol/L
FrequencyAnnually for vegans, every 2-3 years for others over 50

What people actually reported to the FDA

CAERS, 61 reports naming it as the suspect

Most reported effects

Malaise 9
Nausea 7
Pruritus 6
Urticaria 6
Dizziness 6
Named as the suspect 61 reports of 641 that mention it at all
Serious outcome 80% hospitalisation, emergency room or worse
Other Serious or Important Medical Event40
Hospitalization13
Visited Emergency Room11

Reports are voluntary and unverified — they record what someone experienced while taking something, not what the compound caused. Counts skew towards products people take a lot of, and a serious outcome is more likely to be reported than a mild one, so these are not rates. How we filter them →

What actually reaches you

The label counts the carrier, your body does not
Absorption Very high 85 of 100 · best absorbed form of this compound
Delivered daily 0.6 mg
Cost per 10 mg delivered $7.84 comparative — uses the absorption score, not a measured percentage

Works better with

3 documented
+
Folate

Work together in methylation and DNA synthesis

Complementary roles in one-carbon metabolism · level A
+
Vitamin B6

Both involved in homocysteine metabolism

Sequential steps in methylation pathway · level A
+
Betaine

Alternative methylation pathway support

Provides methyl groups for homocysteine conversion · level B

What not to take with Vitamin B12 (Methylcobalamin)

2 documented
!
Vitamin C Megadoses

Very high vitamin C may destroy B12

Oxidative destruction in supplements · mild significance
!
Alcohol

Chronic alcohol use depletes B12

Impaired absorption and increased excretion · moderate significance

Medication interactions

Discuss these with a pharmacist before combining
metformin Moderate

Reduces B12 absorption

What to do: Regular B12 monitoring and supplementation

proton-pump-inhibitors Moderate

Reduces B12 absorption from food

What to do: Consider B12 supplementation with long-term use

nitrous-oxide Major

Inactivates B12 and can cause deficiency

What to do: Avoid recreational use, monitor if medical use

Available forms

bioavailability compared

Best absorbed form of Vitamin B12 — 85% against 3 alternatives. Compare all forms →

Methylcobalamin 85
Adenosylcobalamin 80
Hydroxocobalamin 75
Cyanocobalamin 70

Methylcobalamin: Active form, No conversion required, Better for neurological issues

Adenosylcobalamin: Active mitochondrial form, Better for energy, No conversion needed

Hydroxocobalamin: Longer retention, Good safety profile, Natural form

Cyanocobalamin: Most stable, Least expensive, Most research

Food sources

before you supplement
Clams 84 mcg/100g · 90
Beef liver 70 mcg/100g · 85
Nutritional yeast (fortified) 17 mcg/100g · 80
Salmon 4.9 mcg/100g · 75
Eggs 0.9 mcg/100g · 60

Too little

deficiency signs
  • Fatigue and weakness
  • Megaloblastic anemia
  • Neurological problems (tingling, numbness)
  • Memory problems and cognitive decline
  • Depression and mood changes
  • Balance problems and difficulty walking
  • Glossitis (smooth, red tongue)

Too much

toxicity signs
  • No known toxicity symptoms
  • Possible acne flare-ups at very high doses
  • Rare allergic reactions
  • No upper limit established
  • Water-soluble, excess is excreted

Who benefits most

vegans-vegetarians

B12 is found almost exclusively in animal products

250-1000 mcg daily
elderly-over-50

Reduced stomach acid and intrinsic factor production

500-1000 mcg daily
pernicious-anemia

Autoimmune condition affecting B12 absorption

1000-5000 mcg daily or injections
metformin-users

Metformin reduces B12 absorption

500-1000 mcg daily
fatigue-sufferers

B12 deficiency is a common cause of fatigue

1000-2500 mcg daily

Where to buy it

compare forms first

Look for Vitamin B12 (Methylcobalamin) at 500-1000 mcg per serving. The form that matters here is Methylcobalamin.

Find on Amazon

Affiliate link — we may earn a commission at no cost to you.

What else affects it

Beyond other supplements
!
Alcohol

Chronic alcohol use depletes B12

Impaired absorption and increased excretion

How it works

  • Cofactor for methionine synthase (methylation)
  • Cofactor for methylmalonyl-CoA mutase (fatty acid oxidation)
  • Essential for DNA synthesis and cell division
  • Required for myelin sheath formation and maintenance
  • Supports homocysteine to methionine conversion
  • Critical for red blood cell maturation

Key findings

what the evidence supports
  • Essential for preventing megaloblastic anemia (established)
  • May improve cognitive function in deficient individuals (Cochrane 2018)
  • Critical for nerve function - deficiency causes neuropathy (NEJM 2013)
  • Vegans require supplementation to prevent deficiency (AJCN 2016)

Sources: NIH Examine.com · data reviewed 2026-08-02

Compiled by Denis, who maintains this database and holds no medical qualification — every figure here is sourced or derived, never asserted. How we calculate it →

Common questions

What are the benefits of Vitamin B12 (Methylcobalamin)?

Documented effects: Energy production support; Neurological function; Red blood cell formation; Cognitive function. Essential cofactor in cellular energy metabolism

How much Vitamin B12 (Methylcobalamin) should you take per day?

The common daily range is 500-1000 mcg. By goal — maintenance: 250-500 mcg; therapeutic: 1000-5000 mcg; maximum: No established upper limit; toxic: No known toxicity.

When is the best time to take Vitamin B12 (Methylcobalamin)?

Morning sublingual. First effects are typically reported within 1-2 weeks for energy improvements.

What are the side effects of Vitamin B12 (Methylcobalamin)?

At excessive doses: No known toxicity symptoms, Possible acne flare-ups at very high doses, Rare allergic reactions, No upper limit established, Water-soluble, excess is excreted. Safety rating at normal doses is 10 out of 10.

What should you not take with Vitamin B12 (Methylcobalamin)?

Separate it from Vitamin C Megadoses, Alcohol by two to four hours. Very high vitamin C may destroy B12

Does Vitamin B12 (Methylcobalamin) interact with medications?

Documented interactions with metformin, proton-pump-inhibitors, nitrous-oxide. Discuss these with a pharmacist before combining.

How do you know if you need Vitamin B12 (Methylcobalamin)?

The marker is Serum B12 and MMA (methylmalonic acid), optimal range B12: 400-900 pg/mL, MMA: <0.4 μmol/L. Common deficiency signs: Fatigue and weakness, Megaloblastic anemia, Neurological problems (tingling, numbness), Memory problems and cognitive decline.

Taken for

52 Brain & Focus

Caffeine · DHA · Fish Oil (EPA/DHA)

 62 Energy & Metabolism

Vitamin B12 (Methylcobalamin) · Ashwagandha · Vitamin B12 (Cyanocobalamin)