The pharmacologic action of a drug can be _______ or _______ target.

• A. On-target; off-target
• B. Primary; secondary
• C. Local; systemic
• D. Beneficial; adverse

Answer: (A)

The main idea is that a drug’s effect can occur at the intended target or at other, unintended targets. On-target effects come from the drug hitting the receptor or enzyme it was designed to affect, producing the desired therapeutic result. Off-target effects occur when the drug also interacts with other receptors or pathways in the body, leading to side effects or toxicity. This happens because drugs can lack perfect selectivity or reach different tissues (for example, a medication designed to block a heart receptor may also affect receptors in the lungs or brain). An example is a beta-blocker that targets beta-1 receptors in the heart to reduce blood pressure but also blocks beta-2 receptors in the lungs, causing bronchoconstriction—an off-target effect. Understanding this distinction helps explain why some drugs have both beneficial actions and adverse effects, depending on where and how they interact in the body.