epinephrine

Epinephrine, also called adrenaline, is the hormone behind that sudden jolt you feel when startled — a pounding heart, a flush of energy, heightened focus. It is the adrenal medulla's signature product and the body's chief driver of the fight-or-flight response, prepared in seconds and broadcast through the blood to ready you for sudden danger or exertion.

It is a catecholamine made from norepinephrine by an enzyme (PNMT) found mainly in the adrenal medulla, which is why epinephrine is largely a hormone of the medulla while norepinephrine is mostly a neurotransmitter. Acting on adrenergic receptors throughout the body, epinephrine speeds and strengthens the heartbeat, opens the airways, shunts blood to muscles, and raises blood glucose by promoting glycogen breakdown — coordinated changes that maximize the body's capacity for immediate action.

Epinephrine is also a vital medicine. As a drug it is the first-line treatment for anaphylaxis (severe allergic reactions), where its airway-opening and blood-pressure-supporting effects can be lifesaving, and it is used in cardiac arrest. Because it acts fast and wears off quickly, it is given when an immediate, short-lived effect is needed.