Hello there.  I can understand your concern.  Weight gain is harder than you think. Some people just gain weight easily and find it very difficult to lose, but its opposite in many others. Due to high metabolic rate, people experience difficulty in gaining weight. No there is no medicine to magically make you gain weight. You just have to take a high caloric diet. Kindly consult a general physician in person for further evaluation and management. Best regards. Dr. Anil kumar jain. Bangalore.