<P> MAO - B inhibition reduces the breakdown mainly of dopamine and phenethylamine so there are no dietary restrictions associated with this . MAO - B would also metabolize tyramine, as the only differences between dopamine, phenethylamine, and tyramine are two phenylhydroxyl groups on carbons 3 and 4 . The 4 - OH would not be a steric hindrance to MAO - B on tyramine . Two MAO - Bi drugs, selegiline and rasagiline have been approved by the FDA without dietary restrictions, except in high - dosage treatment, wherein they lose their selectivity . </P> <P> MAOIs started off due to the serendipitous discovery that iproniazid was a potent MAO inhibitor (MAOI). Originally intended for the treatment of tuberculosis, in 1952, iproniazid's antidepressant properties were discovered when researchers noted that the depressed patients given iproniazid experienced a relief of their depression . Subsequent in vitro work led to the discovery that it inhibited MAO and eventually to the monoamine theory of depression . MAOIs became widely used as antidepressants in the early 1950s . The discovery of the 2 isoenzymes of MAO has led to the development of selective MAOIs that may have a more favorable side - effect profile . </P> <P> 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 . </P> <P> A transdermal patch form of the MAOI selegiline, called Emsam, was approved for use in depression by the Food and Drug Administration in the United States on 28 February 2006 . </P>

Drugs that inhibit the activity of monoamine oxidase (maoi)