The older MAOIs' heyday was mostly between the years 1957 and 1970.  The initial popularity of the 'classic' non-selective irreversible MAO inhibitors began to wane due to their serious interactions with sympathomimetic drugs and tyramine -containing foods that could lead to dangerous hypertensive emergencies. As a result, the use by medical practitioners of these older MAOIs declined. When scientists discovered that there are two different MAO enzymes (MAO-A and MAO-B), they developed selective compounds for MAO-B, (for example, selegiline , which is used for Parkinson's disease), to reduce the side-effects and serious interactions. Further improvement occurred with the development of compounds ( moclobemide and toloxatone ) that not only are selective but cause reversible MAO-A inhibition and a reduction in dietary and drug interactions.   Moclobemide , was the first reversible inhibitor of MAO-A to enter widespread clinical practice. 
New uses are still being discovered for a number of psychotropic agents that have been available for some time. Among the more important recent discoveries are the efficacy of the tricyclic antidepressants for panic disorder and agoraphobia with panic attacks; the use of the monoamine oxidase inhibitors for the above disorders and for atypical depression and hysteroid dysphoria; the use of propranolol for anxiety disorders and for uncontrollable violent outbursts; the antianxiety and antipanic effects of clonidine; and the usefulness of lithium in treating schizophrenia and schizoaffective disorder and for emotionally unstable character disorders. In addition to strengthening the therapeutic armamentarium, the author says, the discovery of new drug response patterns helps generate or strengthen hypotheses about the pathophysiology of various psychiatric disorders.