The similar looking substance is acting as a placebo. In other words, a substance that will not have any therapeutic effects on the patient.
A placebo is currently used in the treatment of people with hypochondria, which is a psychological condition in which a person is under a constant belief that he or she is having an illness.
By adding this alternative substance (or placebo), Dr. Bloedorn is trying to address the individual's condition of hypochondriasis.
