What type of inhibitor increases the levels of norepinephrine?

Monoamine oxidase inhibitors (MAOIs) work by inhibiting the monoamine oxidase enzyme, which is responsible for the breakdown of monoamines, including norepinephrine, dopamine, and serotonin. When this enzyme is inhibited, the levels of these neurotransmitters increase in the synaptic cleft, leading to enhanced neurotransmission. Specifically, the increased norepinephrine concentration can improve mood and alleviate symptoms of depression, which is why MAOIs are often used in the treatment of certain depressive disorders.

In contrast, selective serotonin reuptake inhibitors (SSRIs) primarily target serotonin levels without significantly impacting norepinephrine. Serotonin and norepinephrine reuptake inhibitors (SNRIs) do increase both serotonin and norepinephrine levels, but they are not the same as MAOIs in mechanism of action. Benzodiazepines are primarily used for their anxiolytic and sedative effects and do not directly affect norepinephrine levels. Therefore, among the choices provided, the MAOIs are the definitive answer for increasing norepinephrine levels.