The purpose of an antagonist drug is to:

• A. Provide a placebo effect to replace a drug's effect
• B. Block or change the effect of an addictive drug
• C. Block pain receptors throughout the body
• D. Reduce withdrawal effects as one stops taking a drug

Answer: (B)

Antagonist drugs block or alter the effect of a drug by occupying its receptor sites without activating them, so the addictive drug (an agonist) can’t produce its usual effects. This is why antagonists are used to blunt or reverse the effects of substances, such as reversing opioid overdose with naloxone or helping prevent relapse with naltrexone. It's not about producing a placebo effect, and blocking pain receptors across the body isn't the defining role of an antagonist. Reducing withdrawal symptoms isn't the primary aim; in some cases, blocking the receptor can even precipitate withdrawal in someone who is dependent, though antagonists can still be used strategically in addiction treatment to deter use.