Symptoms of High Vitamin B2 (Riboflavin)
Excess vitamin B2 (riboflavin) from dietary sources or standard multivitamin supplements rarely causes any symptoms other than harmless yellow-colored urine. 1
Key Clinical Points
Typical Excess Intake (Dietary/Standard Supplements)
- No adverse effects occur with normal dietary intake or standard multivitamin supplementation
- The only common "symptom" is bright yellow urine, which is completely benign and simply reflects urinary excretion of excess riboflavin 1
High-Dose Pharmacologic Intake (>100 mg repeatedly)
When repeatedly consuming pharmacologic doses exceeding 100 mg, potential toxic effects may include:
- Gastrointestinal symptoms: nausea, vomiting, diarrhea, anorexia 1
- Hepatotoxic and cytotoxic effects: High doses can react with light, forming toxic peroxides and atypical tryptophan-riboflavin adducts that exhibit liver and cellular toxicity 1
Important Context
Riboflavin has an excellent safety profile. The 2022 ESPEN Micronutrient Guideline explicitly states that riboflavin "rarely causes side effects" even at elevated doses 1. Animal studies showed no adverse effects at doses up to 1.0% of diet (equivalent to 900 mg/kg body weight/day in rats) 2.
Rare Allergic Reactions
One case report documented anaphylaxis to riboflavin in a 15-year-old, but this represents an extremely rare allergic phenomenon rather than toxicity from excess intake 3.
Clinical Implications
- No upper tolerable limit has been established for riboflavin due to its low toxicity profile
- Therapeutic doses of 400 mg are safely used for migraine prophylaxis 1
- Doses of 50-200 mg/day are used in metabolic disorders (MADD) without significant adverse effects 1
- Even doses up to 3000 mg/day for 8 months have been tolerated in Parkinson's disease patients 1
Bottom line: Unless you're taking repeated pharmacologic doses well above 100 mg daily, vitamin B2 excess is essentially harmless, with yellow urine being the only noticeable effect.