In pharmacology NA stands for norepinephrine. Norepinephrine is a neurotransmitter that is released primarily in the metanephrinergic nerve endings and to a lesser extent in the adrenal medulla. Norepinephrine has a strong effect on α-receptors on blood vessels, a weak effect on β1-receptors in the heart, and no effect on β2-receptors. It agonizes vascular α1 receptors, causing vasoconstriction and thus an increase in peripheral resistance, producing an elevated blood pressure effect. Norepinephrine is commonly used in early neurogenic shock and hypotension after removal of a pheochromocytoma or during drug intoxication. Diluted and administered orally, this drug causes vasoconstriction of the esophageal and gastric mucosa, producing a local hemostatic effect. Norepinephrine may cause adverse reactions such as local tissue ischemic necrosis and acute renal failure. Norepinephrine is contraindicated in allergic patients, hypertensive patients and pregnant women. Patients should follow the doctor’s instructions to standardize the use of medication, do not self-medication or stopping, in order to avoid delays or adverse reactions.