I was treated for Treatment Resistant MDD for YEARS with every antidepressant and antipsychotic and therapy available all to no avail. Doctors have no choice but to prescribe medications by the trial and error method because there are no definitive tests for MI and because every medication affects every patient differently.
Finally had a manic episode, whether it was caused by the antidepressants or because I'm just a late bloomer. An excellent psychiatrist took over my care and started me on Bipolar meds which work just great.