What term describes the amount of drug needed to obtain the desired effect in about 50 percent of those who use the drug?

• A. Dose
• B. Threshold dose
• C. Effective dose
• D. Lethal dose

Answer: (C)

In pharmacology, we describe how much drug is needed to produce a specific effect across a population with a dose–response curve. The amount that achieves the desired effect in about half of those who use the drug is called the effective dose, often noted as the ED50. This value reflects potency: a lower ED50 means the drug is more potent because less is needed to reach the same effect in 50% of people.

The other terms don’t fit this description: the threshold dose is the smallest amount that begins to produce any effect, the dose is just any given amount of drug, and the lethal dose is the amount that would cause death in a population.