**Core Concept**
Post-vagotomy diarrhea is a complication that occurs after vagotomy, a surgical procedure that involves cutting the vagus nerve, which plays a crucial role in regulating digestive processes. The vagus nerve stimulates the release of gastrointestinal hormones, such as gastrin and secretin, which regulate gastric acid secretion and pancreatic enzyme release.

**Why the Correct Answer is Right**
The correct answer is **Cholestyramine**. Cholestyramine is a bile acid sequestrant that can effectively manage post-vagotomy diarrhea by binding to bile acids in the intestine, preventing their reabsorption, and thereby reducing the amount of bile acids that stimulate intestinal secretion and motility. This leads to a decrease in diarrhea.

**Why Each Wrong Option is Incorrect**
**Option A:** **Metoclopramide** - Metoclopramide is a prokinetic agent that increases gastrointestinal motility, which would exacerbate diarrhea in post-vagotomy patients.

**Option B:** **Loperamide** - Loperamide is an opioid receptor agonist that slows down intestinal motility, but it does not address the underlying cause of post-vagotomy diarrhea, which is an overactive intestinal secretory response.

**Option C:** **Octreotide** - Octreotide is a somatostatin analogue that can reduce gastric acid secretion and intestinal secretion, but it may not be effective in managing post-vagotomy diarrhea due to its variable absorption and potential side effects.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that post-vagotomy diarrhea is often caused by an imbalance in gastrointestinal hormones, particularly an overproduction of gastrin and secretin, which can be managed with bile acid sequestrants like cholestyramine.

**Correct Answer:** C. Cholestyramine