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 Glutathione Side Effects Invigor Medical This Gut Enzyme Helps Turn Urine Yellow and Affects Our Health, Too NLM Musings from the Mezzanine First time taking a multivitamin. Urine is neon yellow and it's freaking me out : r Supplements Urine Color: What Your Pee Says About Your Health