They are not injecting growth hormone to be clear. That is something else entirely. My dd was on HGH.
This is from the Wiki, so take it with a grain of salt of course.
Use in weight loss
A controversial usage of hCG is as an adjunct to the British endocrinologist Dr. A.T.W. Simeons ultra-low-calorie weight-loss diet
[7]. Simeons, while studying pregnant women in India on a calorie-deficient diet, and fat boys with pituitary problems treated with low-dose hCG, discovered that both lost fat rather than lean (muscle) tissue. He reasoned that hCG must be programming the
hypothalamus to do this in the former cases in order to protect the developing ftus, and proceeded to use low-dose daily hCG injections (125 mg) in combination with a customized ultra-low-calorie (500 kcal/day, high-protein, low-carbohydrate/fat) diet to help obese adults lose dramatic amounts of adipose tissue without loss of lean, at a Salvator Mundi International Hospital in Rome, Italy, clinic mainly for celebrities. After Simeons mysterious death, the diet started to spread to specialized centers and via popularization by such as the controversial popular author
Kevin Trudeau (search for hCG in that article for more details).
The controversy proceeds from warnings by the
Journal of the American Medical Association[8] and the American Journal of Clinical Nutrition
[9] that hCG is not safe,
[8] indeed ineffective, as a weight-loss
[10] aid on its own; yet its usage as cited above to increase testosterone production contradicts this assertion, since much late-life male obesity is associated with estrogen dominance and deficient testosterone in the mis-named, so-called
andropause. Furthermore, in the Simeons protocol, it is, as in any diet, the ultra-low-calorie component (caloric deficit) that results in weight loss, if the protocol is followed strictly. hCGs role is supposedly to trigger the hypothalamic lean-protection mechanisms Simeons thought he saw, thus promoting mobilization and consumption of
abnormal,
excessive adipose deposits, while protecting normal adipose and lean tissue from being consumed, with the assumption that these protective hypothalamic mechanisms exist in males as well as females, to be acted upon by hCG.
http://en.wikipedia.org/wiki/Human_chorionic_gonadotropin