**Core Concept**
Depot medroxyprogesterone acetate (DMPA) is a long-acting progestin-only contraceptive injection used to prevent pregnancy. Irregular spotting or breakthrough bleeding is a common side effect of DMPA due to its progestogenic effects on the endometrium.

**Why the Correct Answer is Right**
DMPA works by thickening cervical mucus, preventing ovulation, and altering the endometrial lining. The irregular spotting is thought to be caused by the withdrawal bleeding that occurs when the endometrium sheds in response to the absence of estrogen. Treatment options for irregular spotting in DMPA users typically involve addressing the underlying hormonal imbalance.

**Why Each Wrong Option is Incorrect**
**Option A:** Estrogen replacement therapy might seem like a logical choice to counteract the progestogenic effects of DMPA, but it could actually worsen the irregular spotting by increasing the endometrial proliferation and making it more sensitive to progesterone.
**Option B:** Progesterone receptor modulators (PRMs) like mifepristone could potentially counteract the progestogenic effects of DMPA, but they are not typically used for this indication and may have other side effects.
**Option C:** Switching to a different form of hormonal contraception, such as a combined oral contraceptive or a levonorgestrel-releasing intrauterine system (LNG-IUS), may be effective in treating irregular spotting in DMPA users by providing a more balanced hormonal profile.

**Clinical Pearl / High-Yield Fact**
The irregular spotting associated with DMPA is usually dose-related and tends to resolve on its own with continued use. However, if the spotting persists or is heavy, alternative forms of hormonal contraception may be a more effective treatment option.

**Correct Answer:** A. Estrogen replacement therapy.