Thank you for asking Healthcare majic. My name is Dr Ehsan Ullah & I have gone through your query. First of all , it should be remembered that HCG diet is not recommended by FDA as an over the counter drug due to its potential health care issues and safety risks. your friend s main concern is regarding the abdominal pain... I don t know for which purpose she is using HCG diet as some people are prescribed this for Fertility issues while others use it for weight reduction purposes although Existing evidence does not support the use of human chorionic gonadotropin (hCG) in weight reduction, and the use of hCG for this purpose is not supported by the American Medical Association (AMA) or the American Society of Bariatric Physicians. However, diets that so severely limit calories have risks, such as gallstone formation, irregular heartbeat and electrolytes imbalance Side effects reported with the HCG diet include restlessness, depression, fatigue, irritability, edema (fluid build up ) Breast swelling Another serious concern is thromboembolism (the risk of blood clots forming and blocking blood vessels). The area you mentioned as beneath left side of her chest cage is of Spleen, and if such pains persist then it s advisable to stop the HCG diet and seek medical attention. although pain in this region is not specific or common side effect of HCG diets but HCG has potential risk hormonal imbalance and clot formation which can indirectly affect any organ ... This pain can be from some other pathology too, so clinical evaluation is recommended by the physician to role out the cause Hope this may help you. Let me know if anything not clear. Thanks.