An on-target adverse effect is defined as:

An on-target adverse effect is defined as:

• A. The result of the drug binding to an unintended receptor/target
• B. An immune-mediated reaction
• C. The result of the drug binding to its intended receptor/target, but at an inappropriate concentration, or in the incorrect tissue
• D. A reaction caused by drug-drug interaction

Answer: (C)

On-target adverse effects happen when a drug activates its intended receptor, but toxicity arises because that activation occurs at too high a level or in a tissue where that receptor is also present but not the therapeutic target. In other words, the drug is acting on the right receptor, just in the wrong amount or in the wrong place. This is why the best description is that the adverse effect results from binding to the intended receptor/target, but at an inappropriate concentration or in the incorrect tissue. Immune-mediated reactions involve the immune system and are not about receptor activation at the therapeutic target. Off-target effects come from the drug hitting a different receptor or pathway, not the intended one. Drug-drug interactions cause changes in drug levels or effects through interactions rather than receptor binding per se.

On-target adverse effects happen when a drug activates its intended receptor, but toxicity arises because that activation occurs at too high a level or in a tissue where that receptor is also present but not the therapeutic target. In other words, the drug is acting on the right receptor, just in the wrong amount or in the wrong place. This is why the best description is that the adverse effect results from binding to the intended receptor/target, but at an inappropriate concentration or in the incorrect tissue.

Immune-mediated reactions involve the immune system and are not about receptor activation at the therapeutic target. Off-target effects come from the drug hitting a different receptor or pathway, not the intended one. Drug-drug interactions cause changes in drug levels or effects through interactions rather than receptor binding per se.