What is ED50?

• A. Onset of action
• B. Toxic dose for 50% of the population
• C. Peak blood level
• D. Effective dose for 50% of the population

Answer: (D)

ED50 refers to the dose that produces the intended therapeutic effect in about 50% of individuals. It sits on the dose–response curve as the median point where half of the population experiences the desired effect. This makes ED50 a measure of potency: drugs that require a smaller dose to achieve the effect in 50% of people have higher potency than those needing larger doses. It’s about the relationship between dose and effect, not how fast the drug acts or how high the blood level climbs.

Onset of action is about how quickly a drug starts to work, not how much is needed. A toxic dose for 50% of people (TD50) or a lethal dose for 50% (LD50) describes harmful or fatal effects, not therapeutic effects. Peak blood level (Cmax) is a pharmacokinetic concept describing the highest concentration reached, not the amount needed to produce the desired effect.