Ravenhair has pointed out the crux of the argument - 'rapid' weigt loss doesn't last. Far better is a structured programme of a proper diet, and gentle exercise - your local gym will design a prgramme tailored to your needs, but if finances don't permit, your GP will advise you on both. The trick is to burn off more energy than you take in, but it does take time. Worth it if you can keep the results though.
well, if you are just trying to get into a special dress for one evening, there are various massage/wrap type treatments which claim to make you lose some inches but it is short lived... it comes back on after a few days - or so I heard, as I have never tried.