A methylated B vitamin is a B-complex ingredient sold in its active or coenzyme-style form rather than as a simpler precursor that the body has to convert. The two best-known examples are methylcobalamin as a form of vitamin B12 and L-5-methyltetrahydrofolate (5-MTHF) as a form of vitamin B9 (folate). Methylated forms sit inside the broader vitamin class and are mostly relevant for ingredient label interpretation rather than as a universal upgrade, in the same way that understanding supplement categories describes other label-driven choices.
What "methylated" actually refers to
Methylated forms carry a methyl group that the body otherwise has to attach during normal metabolism. For B12, methylcobalamin and adenosylcobalamin are coenzyme forms, while cyanocobalamin is a stable manufactured form that the body converts. For B9, 5-MTHF is the active form that the body uses directly, while folic acid is a manufactured precursor that goes through one or more conversion steps. Several other B vitamins have active or phosphorylated forms (for example, pyridoxal-5-phosphate for B6, riboflavin-5-phosphate for B2), and labels sometimes group all of these under "activated B-complex."
Where this matters most
For most users with a typical diet and no relevant clinical issue, both methylated and non-methylated forms supply the vitamin in question. For users with known metabolic differences, persistent deficiency despite supplementation, or a clinician-directed reason to prefer the active form, the methylated version may be chosen on that basis rather than as a default upgrade.
What the label has to disclose
The label should list the form by chemical name (methylcobalamin, 5-MTHF, etc.) and the dose in micrograms. Total "vitamin B12 1,000 mcg" without a form is ambiguous, and a "B-complex" line that does not break out per-vitamin amounts is the same problem as any non-disclosing mixture.
Uncertainty and limits
Evidence is limited on whether methylated forms outperform non-methylated forms at matched doses in healthy populations. Evidence is limited on the practical effect of self-prescribed high-dose methylated B vitamins outside a clinician-directed plan.
How this appears in Unfair
Unfair stores the chemical form on each B-vitamin library entry, normalizes dose to a common micrograms unit, and treats a switch between forms as a form change so that response shifts are not silently attributed to a brand alone.
Clinical safety note
Unusual flushing, headache, palpitations, sleep changes, or mood changes after starting a methylated B vitamin can occur in some users and are worth pausing for; resume only after a clinician review when those symptoms are present.