I have never used hair vitamins, but have used a hair treatment call Rene Furterer serum, and you could see the results after about 3-4 weeks.
but only in combination with other things
so you need to take
vitamin c - pureway c
silica - flora silica
all in combination
taurine, in combination with
vitamin D, k2, and vitamin A, together
perhaps a b complex, better than biotin alone. the best is Thorne #12 complex
Before taking any vitamins, you should most definitely take a blood test -the root of your issue may be completely irrelevant from a vitamin deficiency!
Either having artificial hair vitamins better you eat green vegetable daily and fish twice in week. It is best natural hair vitamin sources.