MiraLax is a laxative, hence the "Lax". If you take two packs in a day, you will literally be blowin' it out our *** for a week. In now way, shape or form can it be used for weight loss.
Even if you did, you won't learn anything. In order to lose weight, you have to do it healthily, like exercising and eating fruits and vegetables and not over eating on anything. Taking something to lose it will not gain you those eating habit skills, you'll only lose the weight ( if it does make you lose weight ) just to gain it back and that's called Yo-Yo dieting, which is severely unhealthy for the body, as it puts in through huge amounts of stress. You could seriously have heart attack or organ failure.
Like Fazer said, it's probably more than unhealthy to go onto something like that. It's better off just to do it naturally, even though it's hard. Just keep trying. Also, what helped me lose my weight was keeping track of my daily food. Go to www.MyFitnessPal.com. It really helps.
Methods like that are dangerous. They deny your body nutrients it needs and, in the longer term, cause permanent damage. If you really need to lose weight then diet and exercise is the way to do it safely.