ED50 is defined as what?

• A. The dose required to produce toxicity in 50% of humans
• B. The amount of drug required to produce a specific effect in 50% of animals tested
• C. The maximum effect achieved in 100% of animals
• D. The amount of drug needed to reach peak plasma concentration in animals

Answer: (B)

ED50 is the median effective dose—the dose that produces a defined therapeutic effect in 50% of the population studied. This value comes from dose–response data: when you plot the effect against dose, the ED50 is the dose at which half of the subjects exhibit the specified effect. It reflects potency: a drug with a lower ED50 achieves the same effect at a smaller dose. This concept is about achieving the therapeutic effect, not about maximum effect (that’s Emax) or toxicity (TD50/LD50). It’s also separate from pharmacokinetics parameters like peak plasma concentration (Cmax).