Understanding receptor pharmacology is key to predicting drug effects and answering Step 1 pharmacology questions. Drugs can act as agonists, antagonists, partial agonists, or inverse agonists, each with distinct effects on potency and efficacy.

Key Concepts

• Efficacy (Emax): The Maximum effect a drug can produce.
• Potency (EC50): Amount of drug required to produce a given effect.
• Competitive antagonists shift the dose–response curve to the right (↓ potency, same efficacy).
• Noncompetitive antagonists lower the efficacy but do not change potency.
• Partial agonists have lower efficacy than full agonists, even at high doses.
• Inverse agonists bind the same receptor but decrease baseline activity.

Graphical Summary

1. Competitive Antagonist → Rightward shift (↓ potency, efficacy unchanged).
2. Noncompetitive Antagonist → Downward shift (↓ efficacy, potency unchanged).
3. Partial Agonist → Reduced efficacy compared to a full agonist.
4. Inverse Agonist → Decreases receptor activity below baseline.

Comparison Table

Learning Objective :

Be able to differentiate between competitive antagonists, noncompetitive antagonists, partial agonists, and inverse agonists by recognizing their effects on potency and efficacy and applying this knowledge to clinical drug examples.