If there was a risk of organ failure they'd hardly be so readily available I don't think. Gall stones, as Tracy has already pointed out, can be a side effect of any significant weight loss. They can also be a side effect of being a woman of a certain age (sorry) whether you have lost weight or not. As the doctors say "female, fair, fat and forty" are your risk factors! There are plenty of us here who are taking/have taken Xenical with no problems. Good luck!