Which statement best defines LD50?

• A. The lethal dose
• B. The median effective dose
• C. The threshold dose
• D. The half-life

Answer: (A)

LD50 is the dose that would kill 50% of a defined population under specified conditions. It’s a standard measure of acute toxicity, typically expressed as mg of substance per kg of body weight. This distinguishes it from the median effective dose, which is the dose needed to produce the desired effect in 50% of subjects, not death. It’s also not the threshold dose, which is the smallest amount that produces any detectable effect, and it isn’t the half-life, which describes how long it takes for half of the substance to be eliminated from the body. In short, LD50 defines the lethal dose for half the population under defined testing conditions.