Firstly, you could have a reaction to the medicines, which can cause nausea and skin reactions such as reddening and hives. A tender lump may form in the vein where the IV was placed. This will usually settle spontaneously but you should call your doctor if redness or swelling develops or persists. This is similar to the complication rate of routine upper gastrointestinal endoscopy or sigmoidoscopy. All possible precautions are taken to minimize this risk.
Perforation usually requires prolonged admission.
Passing the needle through the gut wall into the target tissue may cause bleeding but this is usually minor and not serious. Occasionally it is necessary for patients to be admitted for observation but rarely are blood transfusions or surgery required for bleeding. Very rarely patients may develop acute pancreatitis following biopsy of the pancreas. This will require admission to hospital for observation, rest, IV fluids, and pain relief but usually settles spontaneously over a few days. Thus, EUS is a safe procedure and complications are uncommon.