Xenical is a drug used to treat obesity. It won’t burn fat, it works so your body can’t use all the fat you eat as energy, some of it will go strait trough you unaffected by the body’s metabolism. Hence the fatty, sometimes running… No long-term studies has been done, just four year, so there’s no knowledge in how it will affect you in the long run even if you stop taking it. Obesity is in it self so dangerous so some side effects might be of less importance if you lose 50kg or so with it. The fact that there have been raised liver enzymes reported, it does affect your vitamin uptake of especially vitamin E (important antioxidant especially if you are training or freediving). Some allergic reactions are reported as well as breathing difficulties. Ok those are rare but if you are one in a million it doesn’t help if it’s not often seen. I wouldn’t touch it even if I were pretty heavy. As I see it there are many much better ways to treat obesity.
Anyway good luck with your training, weight loss and diving. Let us know how it goes. I’m especially interested in your training program.