 A variety of medically important drugs work by altering the actions of norepinephrine systems . Norepinephrine itself is widely used as an injectable drug for the treatment of critically low blood pressure . Beta blockers , which counter some of the effects of norepinephrine , are frequently used to treat glaucoma , migraine , and a range of cardiovascular problems . Alpha blockers , which counter a different set of norepinephrine effects , are used to treat several cardiovascular and psychiatric conditions . Alpha @-@ 2 agonists often have a sedating effect , and are commonly used as anesthesia @-@ enhancers in surgery , as well as in treatment of drug or alcohol dependence . Many important psychiatric drugs exert strong effects on norepinephrine systems in the brain , resulting in side @-@ effects that may be helpful or harmful . 
