HI, thanks for using healthcare magic Allergic reaction differs from side effects. Side effects are usually listed as possible symptoms that can occur as as result of taking a medication. Eg a medication may list a rash as a side effect, not that the person is allergic to it and it caused a rash but the rash can occur to a small number of persons due to the medication Allergic reaction implies that an individual experienced an allergic response to the medication. Allergic reaction would not be known till the medication is used unless a person is allergic to a very similar med. In terms of the orencia,it affects the immune response/immune system. It suppresses or pushes down the immune system. It is not chemotherapy used for cancer, it is used for autoimmune conditions (where the body is basically fighting against itself) I hope this helps