Depressed mood states are linked to
low levels of serotonin and
low levels of norepinephrine.
It has been shown that serotonin and norepinephrine are involved in depression, the deficit in either neurotransmitter can cause depression. Thus, these neurotransmitters are targeted in antidepressants. For example, Serotonin-norepinephrine reuptake inhibitors are one of the most commonly used class of antidepressant drugs that treat depressive disorders. The mechanism of this drug is to inhibit the reuptake of serotonin and norepinephrine, which results in their higher concentrations.