Adrenaline is a hormone naturally produced in response to exertion or stress by the adrenal gland. Normal endogenous plasma concentrations are within the range of 30 - 160ng/l.

Oral administration of adrenaline results in rapid destruction by the gastro-intestinal enzymes; adrenaline is consequently administered by injection.

Adrenaline acts at both α and β adrenergic receptors to counter the physiological effects of anaphylaxis.

Stimulation of α adrenergic receptors results in vasoconstriction which raises the blood pressure and reduces erythema, urticaria, and angioedema. It is also possible that the vasoconstrictive effect of adrenaline minimises further absorption of the allergen from a sting or injection, although this effect cannot be confirmed.

Stimulation of β adrenergic receptors causes bronchodilation alleviating bronchospasm, wheezing and breathlessness. The β stimulation also increases myocardial output and contractility, further increasing blood pressure. The β stimulant effect also suppresses further mediator release from mast cells and basophils, helping to halt the reaction.