Can prolonged use of prescription drugs cause a mental illness?

It depends: It depends on which prescription drugs you're talking about -- but one mental illness that can happen is addiction. It does not happen automatically, but certainly can with medicines like valium, ativan, klonipin, xanax, (alprazolam) vicodin, etc. Some people abuse these. I have also seen bipolar disorder unleashed by giving an antidepressant without taking an extensive personal and family history.