What are the possible complications of an upper endoscopy?

Uncommon, a bunch. Need to discuss with doc before test. Get info brochure too. There are possible sedation/medication risks, sore throat, bleeding (if biopsy, polyp removal), perforation (rare, about 1:10, 000, unless advanced work, e.g. Forcible dilatation of tight stricture), rarely infection. Talk to md re: meds, supplements, herbals that can interfere with blood clotting, possible need to stop before the test.
Perforation. For a simple upper endoscopy perforation of the G.I. Tract is the most feared complication. If biopsies or other therapeutic interventions are performed then bleeding is also a concern there is also the standard risks associated with moderate sedation which are mostly respiratory in nature.