LD50 represents the dose required to kill 50% of test organisms. Which of the following options best matches this definition?

LD50 represents the dose required to kill 50% of test organisms. Which of the following options best matches this definition?

• A. Dose to kill 50% of test organisms
• B. Dose to kill 95% of test organisms
• C. Dose that causes death in all test organisms
• D. Dose to cause long-term health effects in 50% of subjects

Answer: (A)

LD50 is the median lethal dose: the amount of a substance that, under defined conditions, is expected to kill 50% of a test population. It comes from plotting dose–response data and identifying the point where half the organisms die, representing a statistical average rather than a guaranteed outcome for every individual. This is different from a dose that kills everyone, a dose that causes only long-term health effects, or a dose that kills a higher percentage like 95%.

LD50 is the median lethal dose: the amount of a substance that, under defined conditions, is expected to kill 50% of a test population. It comes from plotting dose–response data and identifying the point where half the organisms die, representing a statistical average rather than a guaranteed outcome for every individual. This is different from a dose that kills everyone, a dose that causes only long-term health effects, or a dose that kills a higher percentage like 95%.