I also have fine/thin hair. When I was young not problems but when I was 20 I was losing my hair, weight gain, menstrual problems etc etc. At that time( I am almost 40 now) I was diagnosed with PCOS- Polycystic Ovarian Syndrome or PCOD as some call it. I have tried sooooo many products and spent lots of $ trying different things but I can tell you that Nioxin has helped me for years. It is true that your don't realise it till you stop using it. The only time my hair got even thicker was when I was pregnant but when my son turned 3 months old, it fell out

At first I felt like a Chia-pet since I saw little sprouts of hair all over. They now make it in various formulas color treated hair etc which is what I use since I get highlights to help with volume I also use the Scalp Therapy which makes you kind of feel like you just brushed your teeth on your head LOL it's quite minty.
I know my hair will never be super thick but I am happy that Nioxin has helped.