Noradrenaline is one of the Neurotransmitters that plays a role in mood changes. If the level of noradrenalines remains low for some reason, then the signal-sending activity becomes low and the person suffers from depression. In such situations, antidepressant drugs are required. These drugs inhibit the enzymes which catalyse the degradation of noradrenaline. If the enzyme is inhibited, this important neurotransmitter is slowly metabolised and can activate its receptor for longer periods of time, thus counteracting the effect of depression. Iproniazid and phenylzine are two such drugs.