The HCG is done with an extremely low calorie diet. People who did the diet alone without the HCG, lost the same amount of weight as those who did the diet with HCG. The difference was in where the weight was lost. Those on HCG lost more weight around the middle of the body.
An extremely low calorie diet may not be a healthy choice and slow down your body's metabolism, which can result in gaining weight on less calories. HCG is a drug and as such may have side effects, some of them long-term. A sensible approach with exercise and mindfulness is always a better approach.