**Core Concept**
The question is testing the association between a specific drug and a cutaneous side effect, specifically hypopigmentation. This is a common phenomenon in dermatology, where certain medications can cause changes in skin pigmentation. The correct answer requires knowledge of drugs that can cause hypopigmentation as a side effect.

**Why the Correct Answer is Right**
The correct answer is likely a drug that inhibits melanin production or interferes with melanocyte function. Pimecrolimus, an immunomodulator used in the treatment of atopic dermatitis, is known to cause hypopigmentation as a side effect. This is due to its mechanism of action, which involves the inhibition of calcineurin, an enzyme that plays a role in the activation of T-cells and the production of pro-inflammatory cytokines. By inhibiting calcineurin, pimecrolimus reduces the inflammatory response, but it can also affect melanocyte function, leading to hypopigmentation.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not have a well-documented association with hypopigmentation.
* **Option B:** This option is incorrect because it is actually known to cause hyperpigmentation as a side effect, not hypopigmentation.
* **Option D:** This option is incorrect because it does not have a well-documented association with hypopigmentation.

**Clinical Pearl / High-Yield Fact**
Pimecrolimus is a topical immunomodulator that can cause hypopigmentation as a side effect, particularly when used on the face. It is essential to monitor patients for skin changes and adjust treatment accordingly.

**Correct Answer:** C. Pimecrolimus