What does M.A.O.I. mean?

Answer 1

MonoAmine Oxidase Inhibitor.

Monoamines are brain chemicals that help alleviate depression. Monoamine oxidase is the chemical that clears out monoamines; so a monoamine oxidase inhibitor prevents the monoamine oxidase from doing its job clearing out monoamines, so the monoamines stick around in your brain longer.

Last line for depression because they've got nasty side effects.