The ED50 is the median effective dose—the dose of a drug that is required to produce a specific effect (e.g., relief from headache) in 50 percent of a given population. The ED50 can be estimated from a dose-effect curve, where the dose of the drug is plotted against the percentage of a population in which the drug produces the specified effect. Therefore, if the ED50s for two drugs in producing a specified amount of relief from headache are 5 and 500 milligrams, respectively, then the first drug can be said to be 100 times more potent than the second for the treatment of headaches.

Bibliography

GILMAN, A. G., ET AL. (EDS.). (1990). Goodman and Gilman's the pharmacological basis of therapeutics, 8th ed. New York: Pergamon.