**Question:** A 43 year old female presented with galactorrhoea. Her investigations show increased prolactin levels. Which among the following condition CANNOT cause increased prolactin secretion?

A. Hypothyroidism
B. Pregnancy
C. Pituitary adenoma
D. Oral contraceptive use

**Core Concept:**

Prolactin is a hormone secreted by the anterior pituitary gland, mainly responsible for stimulating breast milk production in females. The normal physiological regulation of prolactin includes hypothalamic-pituitary-gonadal axis, which ensures that prolactin levels increase during pregnancy and lactation, and decrease in other situations.

**Why the Correct Answer is Right:**

In this scenario, we are considering the possibility of increased prolactin levels due to hypothyroidism (A), pregnancy (B), pituitary adenoma (C), and oral contraceptive use (D).

In hypothyroidism, prolactin levels are typically decreased secondary to impaired hypothalamic-pituitary-gonadal axis regulation. As a result, option A is incorrect.

Prolactin levels are known to increase during pregnancy (option B) and lactation, so this is a correct cause for elevated prolactin levels.

Pituitary adenomas (C) can cause increased prolactin secretion due to the overproduction of prolactin by the adenoma itself.

Oral contraceptive use (D) is another common cause of increased prolactin levels due to the direct effect of oral contraceptives on the hypothalamic-pituitary-gonadal axis, leading to decreased luteinizing hormone and follicle-stimulating hormone secretion. As a result, prolactin levels increase to compensate, which is why oral contraceptive use is a correct cause for elevated prolactin levels.

**Why Each Wrong Option is Incorrect:**

1. **Option A (Hypothyroidism):** Hypothyroidism does not cause increased prolactin levels due to its effect on the hypothalamic-pituitary-gonadal axis, which results in decreased gonadotropin production (luteinizing hormone and follicle-stimulating hormone). As a result, prolactin levels increase to compensate, which is the opposite of what we see in this scenario.

2. **Option B (Pregnancy):** Prolactin levels increase during pregnancy due to the direct effect of progesterone and placental hormones on the hypothalamic-pituitary-gonadal axis. In this scenario, prolactin is increased due to a pituitary adenoma, not pregnancy.

3. **Option C (Pituitary adenoma):** A pituitary adenoma is a pituitary tumor that can cause increased prolactin secretion due to overproduction of prolactin by the tumor itself. In this scenario, the cause of increased prolactin is a pituitary adenoma, not oral contraceptive use.

4. **Option D (Oral contraceptive use):** As mentioned earlier, oral contraceptive use causes