LD50 represents which outcome in toxicology?

• A. The dose resulting in mortality of 50% of the animal population
• B. The dose producing toxicity in 50% of the population
• C. The dose producing therapeutic effect in 50% of the population
• D. The dose causing side effects in 50% of the population

Answer: (A)

LD50 is the median lethal dose—the amount of a substance that will kill 50% of a defined test population under specified conditions. This endpoint focuses on mortality as the toxic outcome, so it’s a measure of acute toxicity and potency: a lower LD50 means the substance is more toxic because a smaller dose is enough to cause death in half the animals. It’s not about nonfatal toxicity or therapeutic effects; those are described by other metrics (for example, ED50 for a desired effect).