Riboflavin 5'-Phosphate (FMN)
Also known as: riboflavin 5'-phosphate sodium, flavin mononucleotide, FMN, R5P, active B2, riboflavin sodium phosphate
Riboflavin 5'-phosphate is the phosphorylated coenzyme form of vitamin B2 (flavin mononucleotide), supplied as its sodium salt. It is far more water-soluble than free riboflavin, which is why liquids and some premixes use it, and it is marketed as an active or coenzymated B2 in premium B-complex products. NIH ODS notes that most supplements use free riboflavin while some use the 5'-phosphate; in the gut it is dephosphorylated to riboflavin before absorption, so the two forms are functionally equivalent as vitamin sources.
Research summary
Hydrolyzed to riboflavin at the intestinal brush border, absorbed, and re-phosphorylated inside cells to FMN and FAD for flavoprotein enzymes.
Dosage
Daily amounts, of compound.
| Lowest studied | Typical range | Highest studied | Upper limit |
|---|---|---|---|
| 1.3 mg | 1.3–25 mg | — | — |
Doses are mg of riboflavin 5'-phosphate sodium as labeled. Roughly 1.27 mg of the sodium salt (MW 478.3) supplies 1 mg riboflavin equivalent (MW 376.4); some labels declare riboflavin equivalents instead, so confirm the basis with the supplier. Same RDA (1.3 mg men, 1.1 mg women) and DV (1.3 mg) as riboflavin, with no UL. The 25 mg typical ceiling is set near the roughly 27 mg single-dose absorption plateau NIH ODS describes, not from a trial of this form; no form-specific dose study was verified.
Standardization: ≥73% riboflavin (as riboflavin 5'-phosphate sodium, USP)
Source material: synthetic (phosphorylated fermentation riboflavin)
Forms of Riboflavin (Vitamin B2)
| Form | Typical dose | Element % | Formats | Price |
|---|---|---|---|---|
| Riboflavin 5'-Phosphate (FMN) | 1.3–25 mg | — | Capsule, Powder, Tablet, Liquid, Gummy | mid |
| Riboflavin (Vitamin B2) | 1.3–400 mg | — | Capsule, Powder, Tablet, Gummy, Liquid | low |
Format suitability
- Capsule
- Powder
- Tablet
- Softgel
- Gummy
- Liquid
Water-soluble and strongly yellow; the preferred B2 for liquid formulas. Hygroscopic; keep dry in premixes.
Formulation notes
Usually paired with other coenzymated B vitamins (P5P, methylcobalamin, L-5-MTHF) in active B-complex products. Light-sensitive.
Sources
Related ingredients
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VitaminCyanocobalamin is the synthetic, highly stable form of vitamin B12 used in most supplements and fortified foods.
Typical: 100–1,000 mcg
Vitamin B12 (Methylcobalamin)
VitaminMethylcobalamin is one of the two coenzyme forms of vitamin B12 that the body uses directly, in this case for the methionine synthase reaction that recycles homocysteine and supports methylation.
Typical: 100–1,000 mcg
Iron Bisglycinate
MineralFerrous iron chelated with two glycine molecules, the form most prenatal and gentle-iron products now use.
Typical: 18–30 mg
Vitamin B6 (Pyridoxine HCl)
VitaminPyridoxine hydrochloride is the standard, inexpensive, and highly stable form of vitamin B6 used in nearly all multivitamins and B-complex products.
Typical: 1.7–50 mg
Iron (Ferrous Sulfate)
MineralThe reference iron salt used in most clinical research and public-health programs, inexpensive and reliably absorbed.
Typical: 18–45 mg