The HCG diet is based on the idea that taking HCG will trick your body into thinking that it is pregnant. Then, when the body finds itself starving for calories it will pull from the fat stores instead of the muscle stores, thus protecting the muscles while burning the fat.
There's not a lot of scientific evidence either way. The dangers of obesity are well known, and includes a higher risk of heart attacks, diabetes and cancer.
But Very Low Calorie Diets (VLCDs) -- diets with less than 1,000 calories -- have been linked to their own litany of health risks, including gallstones and liver and kidney problems.
True HCG diets are conducted under medical facilities and use special foods that are both low-calorie and highly nutritious. Doing a Very Low Calorie or HCG Diet on your own can be dangerous and really should receive medical oversight.
There is no question that a Very Low Calorie Diet can help you lose weight. There's just the dangers of harming vital organs in the process.
"Real" HCG Drops?
Not to disappoint anyone, but "real" HCG drops do not exist. The only true HCG or Human Chorionic Gonadotropin that exists must receive a prescription and be administered as shots under a Doctor's supervision.
Typically, the "Real HCG Drops" you see sold on the internet are a homeopathic remedy -- which is said to contain the "essence" of HCG. By this they literally mean that it has been diluted to the .0000001 level -- and is such a low level of HCG that it cannot be measured by many scientific devices. (Assuming a 3C homeopathic tincture.
Bad With Numbers? Let's put it this way, the HCG Homeopathic remedies are 99.99999% not HCG.
They purport to sell you a solution that contain the "energy" of HCG.
In fact, the FDA just outlawed over-the-counter HCG remedies.