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.