Hello dear, First of all, please do not be in a hurry to gain weight. The body functions according to its metabolic rate, and any measure taken (in the form of pills or supplements) to enhance it will interfere with the normal metabolic rate of the body & causes a number of side effects. So, 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. Despite these measures, if you experience difficulty, it will be better to rule other causes of underweight. Investigations like complete blood count, thyroid profile, estimation of blood sugar level will be helpful to rule out any chronic infection, hormonal and metabolic causes. Wishing you a healthy life. Take care.