http://www.dietscam.org/reports/hcg.shtml
One of the most enlightening books I ever read was by Dr. Dean Edell, a doctor who does television and radio in the SF Bay Area. He was employed as a doctor by an organization giving the HCG shots at centers, and revealed some of the problems with the "science" behind them. He was working at centers based on Dr. Simeon's plan, and openly stated the problems with the shots...that they don't work, that when people complained about energy they gave them saline shots for the placebo effect, etc. Bad news.
There have been over 30 years of studies on HCG. None of them showed any changes in weight loss, except, supposedly, studies conducted personally by Dr. Simeons, who obviously had a financial stake in the results.
Any weight loss is from the 500 calories a day part of the plan, which is dangerously unhealthy. Very Low Calorie DIets (defined as under 800 calories a day) have serious health risks, need to be severely controlled for nutritional deficiencies, and are generally only used in severe cases of obesity where the risks of remaining so obese are greater than the risks of the diet itself.