HCG is a naturally occurring human hormone. Dr. Simmeons, a British endocrinologist, discovered that HCG combined with his diet triggers the body to utilize its own fat stores more readily. Many people have so called "thrifty genes", meaning the less they eat, the more their body will tend to hoard fat. In this case, the body is simply compensating for what it recognizes as a lack of food, which could mean the person is starving, so survival kicks in. HCG helps to bypasses this mechanism for the duration of the diet--the result is the body consumes its own fat stores, especially the stubborn fat that can be so difficult to lose on other types of diets.
Also, the website sells a 15-day supply of hCG drops for $59! You don't even need a prescription. That is because it is a homeopathic solution. In another words, it is not regulated by the FDA and there is no standardization of the purity or concentration. Also, you don't know what else is in the solution. In other words, you may be paying $108 per month for diluted urine.
Many people rave about their success using this diet. But, is it the hCG really fixing your metabolism and curbing your hunger? Or, is it simply the fact that you are on a 500 calorie/day diet? Again, although this diet is popular in 2011, it has been around for the last 40 years. In fact, there is a lot of research on this topic over the last 30 years. While 'fixing your metabolism and adjusting hormones" is sexy and sells supplements, the research is pretty conclusive. Injecting pure (not unregulated drops sold on the internet) hCG DOES NOT improve weight loss or appetite control more than a low calorie diet alone, as demonstrated in random, double-blind, controlled clinical trials. See This study, and This study, and This study. Once you go off the 500 Cal/day diet, guess what happens???
Hey, here is a thought. Why don't you start an appropriate exercise program, including strength training, start improving your nutrition (I would recommend my Food Rules) and commit to making it a permanent lifestyle change?