On a dose–response curve, potency is indicated by how close ED50 or EC50 is to which axis?

On a dose–response curve, potency is indicated by how close ED50 or EC50 is to which axis?

• A. The Y axis.
• B. The X axis.
• C. The origin.
• D. A vertical asymptote.

Answer: (A)

Potency is about how much drug is needed to produce a given effect. The ED50 or EC50 is the dose (or concentration) that gives 50% of the maximal response. If a drug is more potent, you need a smaller dose to reach that 50% effect, so the ED50 moves closer to the vertical axis (the Y axis) on a dose–response plot. In other words, the closer ED50/EC50 sits to the Y axis, the higher the potency. The X axis represents dose itself, so potency is not about being near some other axis or a vertical asymptote; it’s about how leftward the ED50/EC50 shifts toward the Y axis.

Potency is about how much drug is needed to produce a given effect. The ED50 or EC50 is the dose (or concentration) that gives 50% of the maximal response. If a drug is more potent, you need a smaller dose to reach that 50% effect, so the ED50 moves closer to the vertical axis (the Y axis) on a dose–response plot. In other words, the closer ED50/EC50 sits to the Y axis, the higher the potency. The X axis represents dose itself, so potency is not about being near some other axis or a vertical asymptote; it’s about how leftward the ED50/EC50 shifts toward the Y axis.