It turns out that to lose weight and keep it off, you need to eat fewer calories than your body needs to fuel itself. You can cut these calories by eating less or by exercising. Every fad diet plays with this basic fact. The Adkins diet tends to have people eating about 1,200 calories a day, so they're bound to lose weight. If you limit your food options, you're bound to eat less due to boredom. How many bowls of cabbage soup can one person eat in a day?
Now there are doctors prescribing $900 plans that involve daily injections of a pregnancy hormone, HCG. The other part of this diet plan? Reducing your calories to less than 500 a day. For most people, that's going to lead to a weight loss of 2+ pounds a week, without the expensive injections. One patient of this plan lost closer to 8 pounds a week. His starting weight of 230 pounds means that the 500 calories a day would have led to at least four pounds a week without the shots. Possibly more because he's probably losing lean muscle mass along with the fat.
There are no studies out there for the long-term effects of taking a pregnancy hormone when you're a man, or a woman who isn't pregnant. The unknown side-effects of this drug and its new-found popularity have led the FDA to create several videos and a page devoted to HCG. There are some studies discounting it as a good weight-loss aid, though. It is not a good idea to inject yourself for weight loss. Fitness and food should help you get healthier and as a side-effect, thinner. Thin shouldn't be the goal, healthy should be.