**Question:** Drugs which produce gynaecomastia are all EXCEPT:

A. Estrogen
B. Androgen
C. Prolactin
D. Testosterone

**Core Concept:** Gynaecomastia is the medical term for the enlargement of the breast tissue in males, usually caused by hormonal imbalances or exposure to certain medications, chemicals, or conditions.

**Why the Correct Answer is Right:** The correct answer, D. Testosterone, is not correct because testosterone is a male hormone responsible for the development of male secondary sexual characteristics, including the growth of facial and body hair, deepening of the voice, and the enlargement of the penis and testicles. Testosterone does not cause gynaecomastia, but rather exacerbate it in cases where it is already present.

**Why Each Wrong Option is Incorrect:**

A. Estrogen: Estrogen is a female hormone responsible for the development of female secondary sexual characteristics and breast tissue. Although estrogen is commonly associated with gynaecomastia, it is not the only culprit.

B. Androgen: Similar to testosterone, androgens are male hormones responsible for the development of male secondary sexual characteristics. Androgens, including testosterone, are not directly responsible for gynaecomastia but can worsen it.

C. Prolactin: Prolactin is a hormone that plays a role in breast development and lactation. However, prolactin is not directly responsible for gynaecomastia but can contribute to its development in certain cases, e.g., when it is elevated due to certain medications or conditions.

**Clinical Pearl:** To avoid gynaecomastia in patients on estrogen therapy, androgens, or prolactin-raising medications, it is crucial to monitor and manage these hormones and medications carefully. This can be achieved by adjusting the dose, choosing alternative medications, or intervening with treatments targeting the underlying cause of elevated hormones or conditions.