**Core Concept**
Nodular regenerative hyperplasia (NRH) is a rare condition characterized by the formation of regenerative nodules in the liver, leading to obstruction of the hepatic sinusoids and ultimately, liver dysfunction. It is considered a form of non-cirrhotic portal hypertension.

**Why the Correct Answer is Right**
NRH is often associated with the use of certain medications, particularly cyclosporine, tacrolimus, and sirolimus, which are immunosuppressants used in organ transplantation. These drugs can cause endothelial damage and lead to the formation of regenerative nodules in the liver. The exact mechanism is not fully understood, but it is thought to involve the inhibition of endothelial cell proliferation and the promotion of fibrosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because NRH is not typically associated with viral hepatitis. While viral hepatitis can cause liver damage and fibrosis, it does not directly lead to the formation of regenerative nodules characteristic of NRH.
**Option B:** This option is incorrect because NRH is not primarily a condition of aging. While liver function may decline with age, NRH is a distinct pathological entity that is not directly related to the aging process.

**Clinical Pearl / High-Yield Fact**
NRH should be considered in the differential diagnosis of patients with non-cirrhotic portal hypertension, particularly those on immunosuppressive therapy. A high index of suspicion and careful history-taking are essential in making an early diagnosis.

**Correct Answer: C. Cyclosporine.**