median effective dose

(pharmacology) The amount of a drug required to produce a response in 50% of the subjects to whom the drug is given. Abbreviated ED₅₀. Also known as median effective dose.

A term used chiefly to characterize the potency of a drug by the amount required to produce a response in 50% of the subjects to whom the drug is given; also known as ED₅₀ or median effective dose.

Median effective dose is most commonly applied in connection with drugs, but it may be used when various other sources of stimuli, for example, x-rays, are under consideration. The response must be of the kind known as quantal, or all-or-nothing, where the investigator is simply able to report that the response either was or was not elicited.

The median effective dose is a well-defined quantity only when the test animal, the end response, and such factors as the route of injection of a drug and the state of nutrition of the animal are specified.

A dose that, under standard conditions, is effective in 50% of a randomly selected group of subjects.