**Core Concept**
Gynecomastia is a clinical condition characterized by the enlargement of breast tissue in males, often due to an imbalance between estrogen and androgen levels. This imbalance can be caused by various medications, hormonal disorders, or genetic conditions. The underlying pharmacological principle being tested here involves the effect of certain drugs on hormone levels.

**Why the Correct Answer is Right**
Spironolactone is a potassium-sparing diuretic that also has anti-androgen properties. It binds to androgen receptors, thereby blocking the action of androgens like testosterone. This leads to an increase in estrogen levels relative to androgens, causing gynecomastia. Spironolactone's mechanism of action involves competitive inhibition of aldosterone receptors, which results in increased levels of aldosterone, but also has a side effect of increasing estrogen levels. This imbalance is responsible for the development of gynecomastia in some patients.

**Why Each Wrong Option is Incorrect**
**Option A:** Digoxin is a cardiac glycoside used in the treatment of heart failure and atrial fibrillation. It does not have a significant effect on hormone levels or cause gynecomastia. Digoxin's mechanism of action involves inhibition of the sodium-potassium ATPase pump, leading to increased intracellular calcium levels and a positive inotropic effect on the heart.
**Option B:** Metoprolol is a beta-blocker used in the treatment of hypertension, angina, and heart failure. It does not cause gynecomastia and has no significant effect on hormone levels. Metoprolol's mechanism of action involves non-selective blockade of beta-1 and beta-2 adrenergic receptors, leading to decreased heart rate and blood pressure.
**Option C:** Furosemide is a loop diuretic used in the treatment of heart failure and hypertension. It does not cause gynecomastia and does not have a significant effect on hormone levels. Furosemide's mechanism of action involves inhibition of the sodium-potassium-chloride cotransporter in the loop of Henle, leading to increased urine production and decreased blood volume.

**Clinical Pearl / High-Yield Fact**
Spironolactone is a classic example of a medication that can cause gynecomastia due to its anti-androgen properties. It is essential to monitor patients on spironolactone for signs of gynecomastia and adjust the dosage or switch to alternative medications if necessary.

**Correct Answer:** C. Furosemide is not the correct answer as it was not listed as an option.