Thanks for writing to us.
The best way to gain weight is by having a healthy diet.
First of all please visit your doctor to look for any medical reasons for being underweight
Then visit a dietician who can plan your diet well as per your need and life style.
Do regular exercise about 30-45 minutes in a day on most days of the week along with a protein and calorie rich diet.
As far as drugs or protein powders are concerned most of them are unreliable. At present in India there are hardly any medicines that are scientifically proven and have a good and long term safely profile.
Please do not take any such drugs which promise a miracle including the one you are talking about. There were reports in past about nutrigain powder in some controversy and questions were raised about the safety.
Please talk to your primary care
physician and take medicines only after his advice.
I hope this information has been both informative and helpful for you.
Dr. Praveen Tayal