In pharmacology, a drug's interaction with its receptor is often likened to which analogy?

• A. A lock
• B. A key
• C. A code
• D. A switch

Answer: (B)

Think of drug–receptor interactions as the lock-and-key idea: the receptor provides a specific binding site, and the drug acts like a key whose shape and chemistry fit that site. Only the right key can bind effectively, which explains why drugs are selective and why small structural changes can drastically change activity. When the key fits, non-covalent interactions hold it in place and the receptor changes shape to produce a response (or block one if it’s an antagonist). So the drug is best described as the key that fits the receptor’s lock. The other analogies don’t capture the active, specific binding in the same way: a code implies a fixed mapping, a switch implies binary gating, and a lock alone doesn’t convey the active role of the drug.