**Core Concept**
Progestogen Only Pills (POPs) are a type of hormonal contraceptive that primarily contain progestogen as the active ingredient. They work by thinning the cervical mucus, preventing sperm penetration, and also have a local effect on the endometrium.

**Why the Correct Answer is Right**
Progestogen Only Pills act by primarily inhibiting the growth and thickening of the endometrium, making it less receptive to implantation of a fertilized ovum. This is achieved through the action of progestogen on the endometrial glands, reducing the production of glycogen and other nutrients necessary for implantation. Additionally, POPs can also cause changes in the cervical mucus, making it less hospitable to sperm penetration.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because POPs do not primarily work by suppressing ovulation. While they may have some effect on ovulation, their primary mechanism is through the alteration of the endometrium and cervical mucus.

**Option B:** This option is incorrect because POPs do not have a significant effect on androgen levels. They primarily act through the progestogenic pathway, which is distinct from the androgenic pathway.

**Option C:** This option is incorrect because POPs are not primarily used to treat acne. While they may have some beneficial effects on acne, this is not their primary indication.

**Clinical Pearl / High-Yield Fact**
It's essential to note that POPs can be used in breastfeeding women, as they do not affect milk production or the baby's development. This is a key advantage over combined oral contraceptives, which are contraindicated in breastfeeding women.

**Correct Answer: D.**