Common side effects of gastric bypass surgery include dehydration because fluids in the body become abnormally depleted. Drinking a lot of water on a daily basis can help ease symptoms of dehydration such as tiredness, sleepiness, dry mouth, flushing or chills. If not enough water is drunk, dehydration will worsen. If it becomes severe, patients may need to go the hospital to be given vitamin and IV fluids. The development of gallstones is another common side effect of gastric bypass surgery. Doctors may elect to remove the gallbladder during surgery or they may prescribe medication. Constipation and diarrhea are also common. Constipation is often alleviated by increasing the intake of water, and a change in diet helps ease diarrhea.