Hello dear, First of all, please do not make hurry in gaining weight. The metabolism of the body functions at its normal rate & any measures taken to hasten up this process can be harmful. Most of the weight gain supplements are prepared from herbal ingredients & do not have any side effects if taken in the optimum dose. But, before choosing any such 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.