My expertise shows that multi-vitamins in its own generic form doesn't do much. Most of it is excreted. And that's because the forms are the piss poor ones if you follow.
I'll break it down for ya. For vitamins to be effective, they need a chelator. In white people (or black depending on how you see it), we call the vitamin the passenger and a chelator its driver. The vitamin won't do its job or might just not the best way, without the best driver. And what you get from multivitamins is a really crappy driver.
Therefore, I would suggest first doing some research in the best forms of supplements you are looking to take.
Hair loss can be a bunch of different malnutrition states, but before you buy anything (make sure it's not any of the Nature-Made or anything at Walgreens) first look up on Google "Best form of 'insert vitamin name here'" and you should always get a list of the vitamin and possible chelator agents it can be complimented with.