Atomoxetine is indicated for the treatment of Attention-Deficit/Hyperactivity Disorder. The precise mechanism by which atomoxetine produces its therapeutic effects in Attention-Deficit/Hyperactivity Disorder (ADHD) is unknown, but is thought to be related to selective inhibition of the pre-synaptic norepinephrine transporter. Most common adverse reactions are: nausea, vomiting, fatigue, decreased appetite, abdominal pain, and somnolence, constipation, dry mouth, dizziness, erectile dysfunction, and urinary hesitation. Atomoxetine is a substrate for CYP2D6 and hence concurrent treatment with CYP2D6 inhibitors such as bupropion (Wellbutrin) or fluoxetine (Prozac) is not recommended, as this can lead to significant elevations of plasma atomoxetine levels.

Venlafaxine is an arylalkanolamine serotonin-norepinephrine reuptake inhibitor, which is sold under several brand names; one of them is venlafaxine hydrochloride. Venlafaxine hydrochloride is a venlafaxine extended release tablets, which are indicated for the treatment of major depressive disorder (MDD). Efficacy of venlafaxine in MDD was shown in both short-term trials and a longer-term trial in MDD. A major depressive episode (DSM-IV) implies a prominent and relatively persistent depressed mood or the loss of interest or pleasure in nearly all activities, representing a change from previous functioning, and includes the presence of at least five of the following nine symptoms during the same two-week period. In addition, venlafaxine hydrochloride is indicated for the treatment of social anxiety (SAD), also known as social phobia. Social Anxiety Disorder (DSM-IV) is characterized by a marked and persistent fear of 1 or more social or performance situations in which others expose to unfamiliar people or to possible scrutiny the person. Exposure to the feared situation almost invariably provokes anxiety, which may approach the intensity of a panic attack. The feared situations are avoided or endured with intense anxiety or distress. The mechanism of the antidepressant action of venlafaxine in humans is believed to be associated with its potentiation of neurotransmitter activity in the CNS. Preclinical studies have shown that venlafaxine and its active metabolite, O-desmethylvenlafaxine (ODV), are potent inhibitors of neuronal serotonin and norepinephrine reuptake and weak inhibitors of dopamine reuptake.

Droxidopa (Northera, Chelsea Therapeutics) is a synthetic catecholamino acid precursor of norepinephrine indicated for the treatment of orthostatic dizziness or lightheadedness in adult patients with symptomatic neurogenic orthostatic hypotension (NOH) caused by primary autonomic failure, dopamine beta-hydroxylase deficiency, and non-diabetic autonomic neuropathy. Droxidopa was approved as oral therapy in February 2014 under the FDA’s accelerated approval program. Droxidopa is directly metabolized to norepinephrine by dopadecarboxylase. The specific mechanism of action of the drug is not known completely, but it is supposed to exert the pharmacological effects through norepinephrine and not through the parent molecule or other metabolites. It increases blood flow to the brain by stimulating peripheral arterial and venous vasoconstriction.