Riboflavin 5'-Phosphate (FMN)
Riboflavin 5'-Phosphate (FMN) is a tier 2 form of Riboflavin (Vitamin B2), used in 216 on-market products and providing 82.5% elemental riboflavin (vitamin b2) by weight.
Basis: riboflavin-equivalent, free-acid FMN MW 456.35 vs riboflavin MW 376.37 (both confirmed PubChem formulas); the commercial sodium-salt/hydrate form will have a somewhat lower fraction -- approximation
Why this tier: Because FMN is hydrolyzed to riboflavin in the upper gut before absorption (IOM 1998), FMN is not expected to be meaningfully more bioavailable than plain riboflavin at typical doses -- despite marketing as the "active coenzyme form," treated as functionally comparable rather than clearly superior. The widely-repeated "1.3-1.7x more bioavailable" marketing claim could not be traced to a primary RCT.
Source: Institute of Medicine 1998, DRI for B vitamins and choline, ch. 5; Jusko WJ, Levy G. 1967, PMID 6030496