I use it in the form of the product Grapefruit Plus (which is mostly glucomannan and a little grapefruit juice extract). I get it at Wal Mart and most of the grocery stores carry it (it's on a hang card with the Dexatrim and such).
The blockage happens because people didn't drink a full glass of water with it, as the instructions tell you to do.
I've used this product on and off for quite some time, have had no adverse reactions, and it sure does help.
The Grapefruit Plus form of glucomannan comes as a yellow pill (as opposed to a gelcap) and I'm a big fan of the product. I used the psyllium too and like this better.
Just my .02 worth...