Epinephrine

Adrenaline, also known as epinephrine, has the chemical formula C9H13O3N. It is a hormone released from the adrenal glands into the bloodstream, usually in response to pain, excitement, anger, or fear, that increases the level of glucose in the blood. The extra glucose, a key source of energy for body processes, in turn increases rate and force of heart contraction, muscular strength, and blood pressure. These changes cause the body to function at a "higher" level. For this reason, adrenaline is often called the "fight or flight" hormone.

Adrenaline-caused increase blood pressure results from increased heart action accompanied by constriction of peripheral blood vessels. Injectable local anesthetics usually contain adrenaline because it constricts blood vessels in the vicinity of the injection. This prevents the blood from rapidly distributing the anesthetic and prolongs the anesthetic effect in the target tissue. Andrenaline is also used to reduce hemorrahage.

[source: Chemical Principles by H. Stephen Stoker]