Okay....Let me put my Nutritionist/Adjunct Professor Hat on...
I think some of you all are overdoing it...remember:
Water Soluble Vitamins (B's and C's) are excreted in excess very fast...thats Y your pee looks highlighter yellow in color! (B's--> Biotin, Pantothenic Acid, B6, B12, Folic Acid, Thiamin, Niacin, Riboflavin)...and Vitamin C (also known as Ascorbic Acid)
Fat Soluble Vitamins sits a little longer...not overly needed in large quantities (A, D, E, K)...well except Vitamin D we now know....I suggest you all (especially if Pregnant or Breastfeeding) take Vitamin D...
Now...If you're taking a Prenatal or Multivitamin....there is no need to take any extra: Folic Acid
Vitamin C...this can be dangerous in excess
Iron...(extra of this stuff makes the stools green and cause constipation)...unless you have been prescribed extra iron (aka ferrous sulphate) due to anemia for example or your doc says so.....
The jury is up on MSM, extra Biotin, B6, extra B12 (unless your elderly), etc, etc on hair growth....the results are inconclusive...truly.....
Thats just my humble opinion.....I used to think you could do your best to eat a good balanced diet and no vitamin is needed...I don't think that anymore for some nutrients...however....for others...you can certainly overdo it to the point where its not harmful...but a waste time and money wise....
Herbs?other supplements........(Spirulina, chollera, etc) you're on your own....be careful too...these and all vitamins and minerals are active compounds that can have an effect on any meds you may be on!