Many complications exist:
There are MANY gastric bypass complications that can happen, and it is important to know what they are so you can make an informed decision on if you want to go through with the procedure.
First and foremost, you could have an allergic reaction to the anesthetic, something that is commonly not even thought about. The next complication could be excessive bleeding from the cutting. This is major surgery, and while it is an easier one to perform, it is still major surgery, and bleeding can occur.
The next gastric bypass complication that can happen is blood clots. It is important to remember to stay ACTIVE in your day to day activities; a sedentary lifestyle will dramatically increase the chances of you getting a blood clot. Another complication that is very common with this procedure is vitamin and mineral deficiencies. This *will* happen if you don't take a multivitamin, there are a few select people who have gotten away with it, but they wont forever. Take a multivitamin; it is a minor thing that can dramatically improve the way you feel.
Also, as with any surgery, there could be gastric bypass complications due to having a person cutting into your flesh. You can lose mobility in your limbs, extremities, etc....properly research your surgeon before you let him cut into you. There is also the issue of birth complications. You should not get pregnant within the first two years of having the surgery. This is important not only for you, but the life of your unborn baby, don't risk it.
There are also many other risks associated with this surgery, and of course the ultimate fear anyone would have is death. Yes, it has happened. This is a major operation, it gives major results, and it has major risks. Do your research, and as always, remember that this procedure is to be used as a last result and odds are you will have at least one gastric bypass complication.