**Core Concept**
Gynaecomastia is a clinical condition characterized by the enlargement of breast tissue in males, resulting from an imbalance between estrogen and androgen hormones. It can be caused by various factors, including certain medications that disrupt the normal hormonal balance.

**Why the Correct Answer is Right**
The correct answer is Spironolactone, a potassium-sparing diuretic that acts as an antagonist to the androgen receptor. This leads to an increase in estrogen levels, causing an imbalance that results in gynaecomastia. Spironolactone is metabolized to canrenone, which has a higher affinity for the androgen receptor, further contributing to its estrogenic effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Digoxin is a cardiac glycoside used to treat heart failure and arrhythmias. It does not have a significant effect on hormone levels, making it an unlikely cause of gynaecomastia.
**Option B:** Metoprolol is a beta-blocker used to treat hypertension and heart failure. It does not have a known effect on hormone levels, and its use is not commonly associated with gynaecomastia.
**Option C:** Furosemide is a loop diuretic used to treat hypertension and edema. While it can cause electrolyte imbalances, it is not typically associated with gynaecomastia.

**Clinical Pearl / High-Yield Fact**
It's essential to note that gynaecomastia can also be caused by other factors, such as liver disease, testicular cancer, and hormonal imbalances. A thorough medical history and physical examination are necessary to determine the underlying cause of gynaecomastia.

**Correct Answer: C. Furosemide**