**Core Concept**
Acanthosis nigricans is a skin condition characterized by dark, velvety skin patches, particularly in the folds and creases of the body. It is often associated with insulin resistance, obesity, and diabetes mellitus. The condition is thought to be caused by insulin-mediated growth factor 1 (IGF-1) stimulation of skin fibroblasts.

**Why the Correct Answer is Right**
Acanthosis nigricans is often seen as a side effect of certain medications that increase insulin resistance or stimulate IGF-1 production. One such medication is **pioglitazone**, a thiazolidinedione used in the treatment of type 2 diabetes mellitus. Pioglitazone works by activating the peroxisome proliferator-activated receptor gamma (PPAR-γ), which increases the expression of genes involved in glucose and lipid metabolism. This leads to an increase in insulin sensitivity, but also stimulates IGF-1 production, contributing to the development of acanthosis nigricans.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a known cause of acanthosis nigricans.
**Option B:** This option is incorrect because it is not a medication commonly associated with insulin resistance or IGF-1 stimulation.
**Option C:** This option is incorrect because it is not a known cause of acanthosis nigricans.

**Clinical Pearl / High-Yield Fact**
Acanthosis nigricans is often seen in patients with insulin resistance or type 2 diabetes mellitus. It can also be a paraneoplastic syndrome associated with internal malignancies, particularly gastric cancer.

**Correct Answer:** B. Pioglitazone.