Monoamine oxidase or MAO for short is an enzyme that neutralizes certain molecules in your body.
You can see a molecule as a piece of LEGO that is made up of different blocks (the atoms). Just like certain LEGO blocks fit into other LEGO blocks, an enzyme can attach to certain molecules. When it attaches to the molecule it neutralizes it by either slowly breaking it in pieces or to stay attached to it and prevent the molecule from doing anything basically.
Now what harmalas do is present a very tasty piece for the MAO-enzyme to attach to, more tasty than say DMT which it normally likes to attach to, the enzyme just fits better into the harmalas than the DMT.
Harmalas are alse a so called RIMA: Reversible Inhibitor of Monoamine oxidase A. This means that once the enzyme breaks the harmalas apart, it will get loose from it and can go on with it's daily job of breaking down the usual stuff like DMT.
Now there are also some pharmaceutical medicines that make the MAO-enzyme instantly in love with it, so much in love even that the enzyme will not dare to break it in pieces and will never part from it again, ever. Like a long lasting marriage this medicine and the enzyme will stay together until till they die together, or in this case: leave your body.
Once these pharmaceutical medicine get rid of all the MAO-enzymes in your body it takes a certain time for your body to generate a new supply of MAO-enzymes. It takes about two weeks to get back to a normal level, hence the warning with Vyvanse to only take it after stopping with MAOI for two weeks.
So due to this, the harmalas have a much shorter waiting period than those pharmaceutical medicine.
Kind regards,
The Traveler