Riboflavin 5'-phosphate (RFP), also called flavin mononucleotide (FMN), is the active form of vitamin B2. The body can use this form immediately. Standard riboflavin requires a conversion step in the liver. People with certain genetic variations that slow that conversion often prefer RFP.
Cells rely on FMN to run the electron transport chain, which generates energy. Many people take it alongside meals to support this process and to maintain normal skin and hair.
Take RFP with food to improve its uptake. A harmless side effect is bright yellow urine. This color signals that your body is flushing out excess riboflavin.