Ephedrine (EPH) is a sympathomimetic amine commonly used as a decongestant and to treat hypotension associated with regional anaesthesia. Chemically, it is an alkaloid derived from various plants in the genus Ephedra (family Ephedraceae).

Ephedrine is a sympathomimetic amine - that is, its principal mechanism of action relies on its indirect action on the adrenergic receptor system, which is part of the sympathetic nervous system or SNS. Whilst it may have weak agonist activity at alpha- and beta-adrenergic receptors, the principal mechanism is to displace noradrenaline from storage vesicles in presynaptic neurons. The displaced noradrenaline is released into the neuronal synapse where it is free to activate the postsynaptic adrenergic receptors.

An ECA stack is a component found in thermogenic weight loss pills, composed of ephedrine, caffeine and aspirin working to speed up the metabolism and thus cause food energy to burn faster. The ECA stack is a popular supplement taken by body builders before workouts due to the increased amount of energy and alertness.

For many years, the US Coast Guard recommended ephedrine together with an equal 25 mg dose of promethazine to its sailors to combat seasickness. Promethazine manages nausea and ephedrine fights the ensuing drowsiness. Commonly referred to as the Coast Guard cocktail, ephedrine may still be available for prescription for this purpose.