Quoting FKSC;[EBFT]:" Is it okay to take multiple vitamins at the same time? I regularly take one a day womens multi vitamin. ... [snip!] ... multi vitamin. But today I also took acidophilus and biotin. Is it true your body pees out extra nutrients it doesn't need?"
Your body only stores a specific amount of the vitamin so yes once you start taking in too much you will pee out the extra!
edit- you can actually overdose on every vitamin but you should be fine because with our diets today it really isnt common lol