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Epinephrine (adrenaline) is a hormone (chemical messenger) naturally secreted by the adrenal medulla (a gland near the kidneys). It travels in the blood and acts on a wide variety of tissues throughout the body. Most noticeably affected are the cardiovascular and pulmonary systems (heart, lungs and blood vessels).

The main actions of adrenaline are widening of the airways, increasing of heart rate and heart contractile force, narrowing of some blood vessels and the widening of others. These result in hypertension (high blood pressure), accelerated breathing and other reactions associated with what is referred to as the "fight or flight" (more accurately, the four basic animal instincts, "fight, flight, fright or f***") response.

Adrenaline stimulates the body to prepare for action, hence "fight or flight". It can dull perception of things like pain and can often be combined with a local anaesthetic, increasing the duration of anaesthesia due to constriction of efferent vessels. Since this only needs to be a local effect it requires only a low dose of adrenaline. Anaesthesia on its own will work fine.

Artificial adrenaline does carry side-effects if administered in too high a dose. They include hypertension, tachycardia (heart beating too fast) and hyperventilation. Adrenaline should only be given on prescription. Also, it should not be given in any of the following cases:

- If you have a history of heart problems - If you have persistently high blood pressure - If you are or may be pregnant - If it would interfere with any existing medication

Adrenaline also increases blood supply to skeletal muscle and the skin. In these areas it is a vasodilator. If you are having a procedure done that involves piercing, especially in a well-vascularised area (like the genitals or face) then avoid using adrenaline to accompany any other pharmacological intervention.