Why is My Pee Bright Yellow? Yellow Urine Causes & Symptoms Tylenol, Autism, And The Glutathione Connection OC Integrative Medicine Vitamin B supplements, especially those containing riboflavin (vitamin B2), often cause bright yellow or neon colored urine. This happens because excess riboflavin is water soluble and is excreted through urine when the body has Your pee indicates how healthy you are. Here's a guide. : r Biohackers