**Core Concept**
The patient is suffering from non-infective diarrhea, and the prescribed medication, diphenoxylate, is an opioid agonist that works by slowing down gut motility. This action helps to alleviate symptoms of diarrhea.

**Why the Correct Answer is Right**
Diphenoxylate acts by binding to opioid receptors in the gastrointestinal tract, specifically targeting the mu (μ) receptors. This binding action decreases the frequency and urgency of bowel movements by slowing the movement of intestinal contents. The mu receptors are located on the enteric nervous system, which controls gut motility.

**Why Each Wrong Option is Incorrect**
**Option A:** Delta (δ) receptors are targeted by some opioids, but diphenoxylate's primary action is not through delta receptors.
**Option B:** Kappa (κ) receptors are also targeted by some opioids, but diphenoxylate's primary action is not through kappa receptors.
**Option C:** Sigma (σ) receptors are a less understood group of receptors, and diphenoxylate's primary action is not through sigma receptors.

**Clinical Pearl / High-Yield Fact**
Diphenoxylate is often combined with atropine to reduce the risk of abuse, as atropine has no therapeutic effect on diarrhea but can be detected in urine, serving as a deterrent.

**Correct Answer:** C.