I did lose a rather significant amount of hair. I took hair vitamins with biotin a month before I started and used all Nioxin products leading up to the start. Like copyman said, treatment affects everyone differently. My hair started to thin out but I was then afflicted with a rash from hell that included my scalp and I think that had more to do with hair loss than the actual meds. One thing that helps is to have a short layered cut. We girls have a hard time with hair loss and mine was more noticeable to me than to anyone else (at least in the beginning). Really the hair loss has ended up to be one of the lesser of my problems and the hair will grow back. Good luck and don't let it worry you. You won't know how the meds affect you until you start and you may have minimal sx.
No, this is not like chemo therapy where it is a given that you will lose hair. I did not lose any hair but it did do some strange things to it. I would say a small % actually lose a significant amount of hair. I have heard more of people saying their hair thinned out , got curly or straight. Everyone reacts different with these drugs.