**Core Concept**
Pirenzepine is a selective M1 muscarinic receptor antagonist. It primarily targets the muscarinic acetylcholine receptors in the stomach, reducing gastric acid secretion.

**Why the Correct Answer is Right**
Pirenzepine works by competitively inhibiting the action of acetylcholine at M1 receptors in the gastric parietal cells, thereby decreasing the release of gastric acid. This results in a reduction of gastric acid secretion, making it a useful treatment for conditions like peptic ulcers and gastroesophageal reflux disease (GERD). The selective action on M1 receptors minimizes the side effects associated with non-selective muscarinic antagonists.

**Why Each Wrong Option is Incorrect**
**Option A:** Pirenzepine is not used for treating hyperthyroidism, as it does not affect thyroid hormone production.
**Option B:** Pirenzepine is not a beta-blocker, and its mechanism of action does not involve the blockade of beta-adrenergic receptors.
**Option C:** Pirenzepine is not used for treating cholinergic toxicity, as it would actually exacerbate the condition by blocking acetylcholine receptors.

**Clinical Pearl / High-Yield Fact**
Pirenzepine's selective action on M1 receptors makes it a useful alternative to non-selective muscarinic antagonists, which can cause dry mouth, blurred vision, and other anticholinergic side effects.

**Correct Answer:** B. Pirenzepine is used for reducing gastric acid secretion in conditions like peptic ulcers and GERD.