What is the ED50 on the Dose-Response Curve?

• A. The median effective dose, the lower the ED50, the higher potency
• B. The dose that produces 50% of maximum response
• C. The lethal dose for 50% of individuals
• D. The dose that produces the maximum response

Answer: (A)

On a dose–response curve, the ED50 is the dose that produces 50% of the maximum possible effect in the population. This point marks the midpoint of the curve and is how potency is compared: a lower ED50 means the drug reaches that 50% effect with a smaller dose, indicating higher potency. It is not the dose that yields the maximum response (that would be the dose at Emax) nor the lethal dose for 50% of individuals (that’s LD50). Some texts call ED50 the median effective dose, which aligns with the idea of a 50% effect across individuals.