Methylcobalamin (B12) vs Methylfolate (5-MTHF)

Mechanism

Methylcobalamin serves as a cofactor for methionine synthase, transferring a methyl group from 5-MTHF to homocysteine to regenerate methionine and subsequently SAMe. Adenosylcobalamin (the other active B12 form) is a cofactor for methylmalonyl-CoA mutase in mitochondrial energy production and odd-chain fatty acid metabolism. B12 is essential for myelin synthesis, DNA synthesis (thymidylate synthase pathway), red blood cell maturation, and neurological function. Deficiency causes megaloblastic anemia and irreversible subacute combined degeneration of the spinal cord.

Standard Dosing

1000-5000 mcg methylcobalamin daily (sublingual preferred)

Timing

Morning, sublingual for best absorption (bypasses intrinsic factor requirement). Can combine with methylfolate.

Cycle Duration

ongoing

Side Effects

• Acne/skin breakouts (common)
• Anxiety (overmethylation in susceptible individuals)
• Diarrhea
• Headache
• Hypokalemia (during rapid repletion of severe deficiency)

Contraindications

• Leber's hereditary optic neuropathy (cyanocobalamin specifically; methylcobalamin is generally safer)
• Polycythemia vera

Best Stacking Partners

Mechanism

5-methyltetrahydrofolate (5-MTHF) is the biologically active form of folate and the primary methyl donor for remethylation of homocysteine to methionine via methionine synthase (requires B12). This reaction generates SAMe (S-adenosylmethionine), the universal methyl donor for >200 methyltransferase reactions including DNA methylation (gene expression), histone methylation (epigenetics), neurotransmitter synthesis (serotonin, melatonin, norepinephrine), creatine synthesis, and phospholipid methylation (phosphatidylcholine). 5-MTHF crosses the blood-brain barrier via folate receptors.

Standard Dosing

400-800 mcg daily (general health); 5-15mg for depression/MTHFR homozygous

Timing

Morning with B-complex. Start low and titrate up, especially in COMT slow metabolizers.

Cycle Duration

ongoing

Side Effects

• Anxiety/irritability (overmethylation, especially COMT slow)
• Insomnia
• Headache
• Joint pain
• Nausea
• Depression paradoxical worsening (overmethylation)

Contraindications

• Active methotrexate cancer therapy (discuss with oncologist — leucovorin rescue is different)
• Untreated B12 deficiency (folate can mask B12 deficiency, allowing neurological damage to progress)
• Some COMT slow metabolizers may not tolerate high doses

Best Stacking Partners