Fitzy...I have always had shedding hair. I never thought it was the pentasa until I came back to it from my medication vacation. Everyone on here was posting that increasing your folic acid helps stop some of the shedding. I take a small amount of folic acid, but I don't know if it is making a dofference for me.
My big thing I found is paying attention to my diet. If I am also going very low fat, the thinning gets worse. I also found it happens more when I am on the dehydrated side. I think both low fat and dryness are messing with the hair cuticle. Finally, I use cheap gentle shampoos and try to give my scalp a break if I can go without washing one day (you know---hide in the house, no one can see me day)