I buy mine online from puritans pride for a really great price since they always have deals on like by 2 get 3 and such...it can be purchased in local health food stores but it's more pricy from my experiance.
I take it in cap form, when I first started though, I took it in liquid form which was absolutely disgusting but very affective (the pills I take are as well)...the caps I take are 500mg I believe.
It's 100% non-toxic which is why my GI said to continue taking it daily and indefinitely if I wanted to, which I am still, almost 6 yrs later.
Early on when I first started taking the caps, I didn't take any one day to see what, if anything, might happen, first thing that came back was bleeding so obviously I started taking them right away again and haven't stopped.
This is my experiance with it, it may be different for others,there are no guarantees, but the guy who told me about it said it put his crohns right into remission and he didn't even have to keep taking them daily anymore.
My bum is broken....there's a big crack down the middle of it! LOL :)