What is the target substance in the body that a drug interacts with?

• A. Enzyme
• B. Carrier
• C. Membrane channel
• D. Receptor

Answer: (D)

Drugs exert their effects by binding to receptors — the proteins that recognize signaling molecules and translate that binding into cellular responses. A receptor can be on the cell surface or inside the cell, and when a drug attaches, it can activate or block the receptor’s signaling pathway, creating the observed effect. While drugs can also interact with enzymes, carriers, or membrane channels, the most fundamental and common target described here is the receptor, because receptor binding initiates the primary pharmacologic response.