Yes, the vitamins do come out in your pee. That's why I'm skeptical about biotin. First of all, biotin is produced in our intestines already. Secondly, a lot of foods have biotin in it, so we most of us must get biotin from what we eat. Then in multivitamins I get more biotin. The last and most important thing is that biotin is a b vitamin. If you get more of a b vitamin than you need, it comes out in your urine.
I dunno... maybe it does work, but it doesn't make sense to me.
And I think that you can develop kidney stones or some kind of mineral deposits somewheres from getting too much over time. I'm not 100% on that though, but otherwise getting too much vitamin b isn't bad for your health, the excess just doesn't get used.