Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Diabetes itself a cause of impotence if sugar levels are uncontrolled. Yes HCG can cause impotency but it is temporary.But still I would suggest him to use diet control and exercises to reduce the weight. Maintain the proper blood sugar levels. Reduce the mental stress by exercises and relaxation. Take nutritive diet reduce carbohydrate content in diet. Drink plenty of water. Hope I have answered your query. Let me know if I can assist you further.