Hi
Thanks for the question. There is no problems with these pills as such since they have a higher bio availability of the vitamins and minerals that your body require and more easily absorbed. You need to take these supplements based on your requirements and goals. Your height and weight, medical history and several other factors will determine how much you should take.
As far as hair greying is concerned there is no clinical evidence that
B12 causes greying. You should only take b12 if your body is deficient in it. But unfortunately it will not stop your greying or hair loss.
I wish I could have told you something differently. Anyway I hope this helps.