Human Chorionic Gonadatrophin (hCG) is the hormone / glycoprotein produced by pregnant women. Dr Simeons first began using hCG in conjunction with a very low calorie diet (VLCD) in the 1950s. His results with obese patients were phenominal. It has been used for weight loss since this time.
hCG is a complex amino acid, which appears to have an effect on both males and females to use abnormal fat reserves for energy. The mechanism by which it works is unclear but it appears to have an effect on the hypothalamus. This gland is like a a master gland which acts to regulate many other important glands and thereby hormones. When hCG is combined with a VLCD the effect is to shift stubborn, often hormonally charged fat deposits.
So you not only shift weight, you shift it from from the areas you may have never been able to shift before. Typically in women it is the love handles, thighs and bottom and in men it is the tummy. In women it is generally the oestrogen / progesterone hormones and these are resposible for the fat on hips and thighs. In men the primary hormone in play is cortisol, the stress hormone.