Adrenergic drugs are also called sympathetic nervous system (SNS). It prepares the body for fright, flight or fight. It is distributed from the thoracolumbar outflow, i.e. T1 to L2–L3. Their ganglia are prevertebral, paravertebral, terminal and adrenal medulla. Major neurotransmitter of SNS includes noradrenaline (NA) and dopamine (DA). A small fraction is metabolized by catechol-Omethyltransferase (COMT) in synapse. Adrenergic receptors were classified by Ahlquist. They are classified into chemical classification, based on mechanism, and therapeutic classification. Catecholamines include adrenaline, noradrenaline, isoprenaline, dopamine, dobutamine, and fenoldopam. Noncatecholamines are devoid of catechol nucleus. They act by direct stimulation of adrenergic receptors and indirectly by releasing noradrenaline (NA). Vasopressors, nasal decongestants, selective β2 stimulants, and anorectics (appetite suppressants) are also discussed in this chapter.