MAOIs, or Monoamine Oxidase Inhibitors, are a class of medications primarily used to treat depression and certain other mental health conditions. They work by inhibiting the activity of the enzyme monoamine oxidase, which is responsible for breaking down neurotransmitters like serotonin, norepinephrine, and dopamine in the brain. By preventing this breakdown, MAOIs can increase the availability of these important chemicals, leading to improved mood and other therapeutic effects.