Although all of the risks involved in gastric bypass surgery aren't fully known, there are many that are. These include possible infection, clotting of the blood, and the development of gallstones, a bleeding ulcer and even pneumonia. It certainly isn't a simple procedure and complications may occur as with all invasive medical procedures.
Before the surgery is performed your doctor or physician will inform you of all the risks, but ensure that you ask all the questions to put your own mind at ease. He/She will also carry various examinations to ensure you're ok for the gastric bypass surgery.
The main risks associated with the gastric bypass are as follows. As the food will be moving from your stomach to the intestines quickly you may get what's called dumping syndrome - symptoms of this include sweating, fainting and diarrhoea. You may also experience vomiting after drinking or eating as if you search the Internet you will find many stories of this which is called stomal stenosis, when there's a tightening of the opening between the stomach and the intestines.
You can reduce the symptoms of dumping syndrome by sticking to the strict diet guidelines given to you by your surgeon. Osteoporosis and bone disease can also occur, but is very rare.
As with all medical procedures there are many risks associated with it, and you should talk to your doctor about any concerns about the gastric bypass surgery. The information here isn't to replace professional advice.