**Core Concept**
The question tests the student's knowledge of antidiabetic drugs, specifically their effects on body weight. **Antidiabetic medications** can be classified based on their mechanism of action and side effects, including weight gain or loss.

**Why the Correct Answer is Right**
The correct answer is a drug that promotes **glycosuria**, increasing glucose excretion in the urine, thereby reducing blood glucose levels without causing weight gain. This class of drugs includes **SGLT2 inhibitors**, which work by inhibiting the sodium-glucose cotransporter 2 in the kidney.

**Why Each Wrong Option is Incorrect**
**Option A:** Typically causes weight gain due to increased insulin levels and **anabolic effects**.
**Option B:** Often leads to weight gain due to increased **insulin sensitivity** and **glucose uptake** in tissues.
**Option D:** May cause weight gain due to increased **insulin secretion** and **glucose utilization**.

**Clinical Pearl / High-Yield Fact**
It's essential to consider the effect of antidiabetic drugs on body weight, as weight management is a crucial aspect of diabetes care. **SGLT2 inhibitors** are a valuable option for patients who need to lose weight or avoid weight gain.

**Correct Answer:** D. Metformin