Hello dear, As you are having difficulty in gaining weight, it is better to rule out causes of underweight. Investigations like complete blood count, lipid profile, estimation of blood sugar level, serum electrolytes, Thyroid profile, will be helpful to rule out any chronic infection, hormonal and metabolic causes. It is not advisable to take any medication or supplement for gaining weight & building muscles, because: 1. The medications interfere with the normal metabolic rate of the body & causes a number of side effects 2. The individual tends to lose more weight after stoppage of the medication. Before choosing any such medication or health supplement, it is advisable to consult your family physician once. Moreover, you should not compromise on routine healthy food such as: 1. Consume more of natural diet like fresh fruits, green vegetables, milk, eggs, wheat, etc. 2. Avoid oily and junk food. 3. Stay away from smoking & alcohol. Wishing you a healthy life. Take care.