 These are drugs whose primary effects are thought to be mediated by different neurotransmitter systems ( dopamine for stimulants , serotonin for antidepressants ) , but many also increase levels of norepinephrine in the brain . Amphetamine , for example , is a stimulant that increases release of norepinephrine as well as dopamine . Monoamine oxidase inhibitors are antidepressants that inhibit the metabolic degradation of norepinephrine as well as serotonin . In some cases it is difficult to distinguish the norepinephrine @-@ mediated effects from the effects related to other neurotransmitters . 
