How MAOIs work. Monoamine Oxidase Inhibitor Antidepressants (MAOIs) work by binding with and stopping the activity of monoamine oxidase, an enzyme found throughout the body.Monoamine oxidase breaks down a number of chemicals made and used by the body and brain.AOIs also increase the amounts of other chemicals in the body and especially some chemicals which are found in food and other medications. Because they increase chemicals other than noradrenaline and serotonin MAOIs can have serious and dangerous side effects if you are not careful about certain foods and other drugs.