Why is your urine bright yellow after you take a multi vitamin?

From Coloring dyes. Most multivitamin have coloring agent added to them ie yellow number 5 or something similar and this non toxic coloring agent is removed unchanged by the kidneys. Urine color can be yellow, green, orange etc depending on the coloring agent added to the multivitamin tablets.
Riboflavin. Most multivitamins contain riboflavin which is eliminated in the urine and is colored yellow.

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