← The FormularyLong gameRiboflavin
Also known as Vitamin B2It turns your urine yellow. That is not the effect.
Riboflavin's most visible effect is cosmetic and irrelevant: it dyes urine a fluorescent yellow, which people routinely read as evidence the supplement is 'working' when it is evidence the supplement is leaving. Deficiency is uncommon on a mixed diet. The one genuinely interesting separate finding is migraine: high-dose riboflavin, around 400 mg a day, has reasonable trial evidence for reducing attack frequency — a dose three hundred times the requirement and a conversation to have with a doctor, not a reason to read anything into a B-complex.
A yellow-orange water-soluble vitamin, present in dairy, eggs, almonds and fortified grains. It is the reason a B-complex changes the colour of your urine.
Riboflavin becomes FAD and FMN — electron carriers that shuttle energy through the respiratory chain. It also sits upstream of other B vitamins: without enough riboflavin, the body cannot properly activate B6 or convert folate, which is why the B vitamins are usually supplied together rather than alone.
Forms the two flavin coenzymes the body uses throughout energy metabolism, and helps regenerate the antioxidant glutathione.
Anyone on a restricted or dairy-free diet. Everyone else is almost certainly covered by food.
Daily inside the complex. Light destroys it, which is why milk is not sold in clear bottles any more.
Yellow urine, and nothing else, unless you were deficient.
Grade A as an essential nutrient; no tolerable upper limit set. Separately, riboflavin at about 400 mg/day has shown benefit for migraine prophylaxis in randomised trials — a pharmacological dose, unrelated to the nutritional amounts in a B-complex.
Read the labelHarmless in excess — the bright yellow urine is riboflavin being excreted, not a sign of anything. Not a treatment for migraine without a doctor's involvement.
Evidence grades describe how well an ingredient is studied — A well-supported, C emerging — not a promise of results. Educational, not medical advice. Doses are typical ranges; follow the label on the product.