The HCG diet is a 500 calories diet taken from the list of high proteins, nutrient rich foods. It can help you achieve the desired weight loss goals if taken in the balanced form. Usually, there are no side effects or worst happenings associated with taking this diet. But, in certain cases it could lead to some negative effects like constipation, headache, leg cramps, dizziness, rash, hair thinning and other concerns like gallstone formation and heart problems like arrhythmia or palpitations. Hence, the diet is not meant for children, pregnant women, breastfeeding women and anyone with preexisting medical condition.