What are the causes for Barium Swallow?

A barium swallow is generally a safe test, but like any procedure, there are occasionally complications. Your doctor should be advised of problems so you can be treated right away. Following are some of these complications:
  • Allergic reaction or anaphylaxis may occur in people who are allergic to the barium drink.
  • Constipation may develop.
  • You may accidentally get barium into the trachea (windpipe). The medical term for this is aspiration.

Source: http://www.emedicinehealth.com