I'm a 22 years old Female who is extremely over weight. Actually Obese! I tried about everything, exercise, eating less and healthfully for the past 2yrs, I've even taken some diet pills to see if they would reduce my weight. Nothing has worked for me to this date. My weight problems have caused me low self-esteem to the point where I give up on life! I left school when I couldn't take the mockery and the staring of other people due to my body size. I know I should be happy with the Way Allah Made me, but I'm not, I'm so depressed, I dropped school, I don't work and most of the time I'm locked in my room, daydreaming my life away. Now I'm considering surgery to loose weight. It's called "gastric bypass" you loose weight by reducing the size of your stomach to 1/3 of it's Original size. What I want to know is this Haram or Halal? I'm doing it to better my self-esteem and health as well. Even though I don't have any health problems beside the excessive weight gain, I'm Healthy, Al-hamdulillah, but I may develop diabetes, heart problems, kidney failure etc. If I don't control my weight now. I really would like to do this if it's permissible in Islam?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

There is no harm in undertaking the surgery mentioned in your question to reduce your weight, provided it does not cause any harm. If it causes any harm it becomes forbidden, since a harm should not be removed by causing another harm.
There is no evidence proving such surgery is forbidden. Moreover, this surgery is not considered as changing the creation of Allah.
Allah knows best.