Define dose-response curve and explain what LD50 and ED50 represent.

• A. A dose-response curve shows the relationship between dose and effect; LD50 is the lethal dose for 50% of the population; ED50 is the dose for 50% of the population to show a specified effect.
• B. LD50 is the dose for 100% lethality; ED50 is the dose for 0% effect.
• C. They are not related to toxicology.
• D. LD50 and ED50 are both equal to the NOAEL.

Answer: (A)

Understanding how a substance’s dose relates to the effect it causes is the key idea here. A dose-response framework plots dose on the x-axis and the resulting effect on the y-axis, showing how increasing exposure changes the outcome. In this context, LD50 is the dose that would kill 50% of the tested population, which provides a standard measure of acute toxicity and allows comparison of how toxic different substances are. ED50 is the dose that produces a defined effect in 50% of the population—this is a useful way to describe the potency for a specific, non-lethal outcome (such as pain relief, sedation, or another endpoint). These median-effect points help compare how strong a substance is for a given outcome and how the curve shifts with different substances or conditions. They’re distinct from NOAEL, which is the highest dose at which no adverse effects are observed. The other statements misstate these concepts: LD50 is not for 100% lethality, ED50 is not for 0% effect, and both are indeed part of toxicology.