What term describes a drug that blocks or changes the effect of an addictive drug?

• A. Tolerance
• B. Withdrawal
• C. Antagonist
• D. Reinforcement

Answer: (C)

The idea being tested is what we call a substance that blocks or changes how another drug works at its target. An antagonist is a drug that binds to receptors but does not activate them, so it prevents the addictive drug from producing its usual effect or alters the outcome. For example, opioid antagonists like naloxone or naltrexone occupy opioid receptors and blunt the rewarding effects of opioids, which reduces reinforcement and use. Tolerance involves needing more of a drug to achieve the same effect, not blocking it; withdrawal is the set of symptoms when stopping, and reinforcement is the process by which the drug’s effects promote continued use. So the correct term is antagonist.