I have tried a few kinds - the rather feeble looking herbal types you find in Boots and some more expensive ones from a sports science company. I found that the ones containing iodine (eg ones made from kelp) gave me a great energy boost after a nasty bout of post-viral fatigue, but I do have a fairly low level of naturally produced thyroxine anyway so chances are if things are normal in your body you won't notice a huge difference. Ingredients like green tea and dandelion root, found in Metasys and Adios, are known to speed food through your system so will make you feel less bloated, and the ones used by professional bodybuilders were expensive but really did work - when I dieted seriously I would take them if I'd had a day where I lost control a bit and ate stuff I shouldn't and they always stopped me putting weight back on. BUT, and this is a big but, they can't be the crux of your weight loss plan. I always found them invaluable in making weight loss easier but I could never have shed a significant amount of weight using them alone - perhaps two or three pounds but no one will ever notice that. When combined with dieting and exercise I really noticed a difference in the speed of my weight loss compared with diet and exercise alone, but I don't think you'll have any luck trying to make significant changes to your body without significant effort unfortunately.