hCG itself, human chorionic gonadotropin, is probably fairly harmless when taken in the low dosages "suggested" for weight loss. It is a placebo of course, but that's a different subject. What I want to talk about here are the dangers not of hCG itself but of the eating plan that is commonly known as "The hCG Diet".
Below is an example of the sort of meal plan that is associated with the hCG diet
Let's take a look at that diet in a more concrete way. The lunch (or dinner) might look something like what I have shown below
A Typical "Meal" on the hCG Diet.
(You only get two of these per day and eating the playing cards is optional)
So what sort of a meal IS this? Well, the answer depends of course on context. The selections I have shown above might make a reasonably healthy and very light lunch. There is nothing intrinsically wrong with this meal. But what if two of these meals is ALL you get to eat every day for many weeks? What then?
Well, THEN things get worrisome. First of all, this is a low-carbohydrate diet. Second, it is a very low calorie diet. So within days of only eating two of these meals per day, you will enter the semi-starved metabolic state called ketosis. Again, ketosis isn't intrinsically dangerous, but it can cause massive diuresis (water loss) and while you're busy urinating-out water, you're also losing a fair number of electrolytes the most important of which is potassium. Excessive potassium loss is very dangerous since potassium is a crucial electrolyte for all cellular metabolism. Lose too much and you'll develop arrythmias (abnormal heart beats); lose more and you'll die. Is massive potassium loss common with the hCG diet? It probably is. Do many people die from it? No. But it is a real risk. It is a real risk with any unsupervised very low calorie diet. If you plan on doing a very low calorie diet, you have to have regular and frequent electrolyte monitoring.
So again, hCG itself probably isn't dangerous--just ineffective for weight loss-- but the diet that is being recommended along with hCG can be dangerous.