Distinguish antagonists and agonists with examples.

Explanation

### Step-by-Step Solution

1. **Definition of Antagonists**: Antagonists are drugs that bind to receptor sites but do not activate them. Instead, they inhibit or block the biological response that would normally occur if the receptor were activated by an agonist or a natural messenger.

2. **Mechanism of Action of Antagonists**: When an antagonist binds to a receptor, it prevents other substances (like agonists or natural ligands) from binding to that receptor. This results in no biological response, meaning that the intended effect of the receptor activation is inhibited.

3. **Example of Antagonist**: A common example of an antagonist is **Naloxone**. Naloxone is used to counteract the effects of opioid overdose by blocking the opioid receptors, thereby reversing the effects of opioid agonists like morphine.

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