**Core Concept**
The question tests the student's knowledge of antidiabetic medications and their effects on body weight. **Antidiabetic drugs** can have varying effects on weight, depending on their mechanism of action. Understanding these effects is crucial for managing **diabetes mellitus** and its complications.

**Why the Correct Answer is Right**
The correct answer is related to medications that increase **glucosuria**, enhance **glucagon-like peptide-1 (GLP-1)** activity, or affect **insulin sensitivity**. These mechanisms can lead to a reduction in body weight. For instance, **SGLT2 inhibitors** promote glucosuria, resulting in weight loss.

**Why Each Wrong Option is Incorrect**
**Option A:** Typically causes weight gain due to increased insulin levels.
**Option B:** May cause weight gain or have a neutral effect on weight.
**Option D:** Often leads to weight gain due to increased insulin resistance.

**Clinical Pearl / High-Yield Fact**
Remember that certain antidiabetic drugs can cause weight loss, which is beneficial for patients with **type 2 diabetes** who are overweight or obese.

**Correct Answer:** D. Metformin