**Core Concept**
Emergency contraception refers to the use of medications or devices to prevent pregnancy after unprotected sex or contraceptive failure. Various hormonal and non-hormonal methods are available, but their efficacy and safety profiles differ. Understanding the pharmacological properties of these agents is crucial for selecting the most appropriate emergency contraception method.

**Why the Correct Answer is Right**
The correct answer is **D. Estrogen**, as estrogen-based emergency contraceptives are not commonly recommended due to potential side effects and interactions with other medications. Estrogen can increase the risk of thromboembolic events, which may be a concern in emergency situations. In contrast, progestin-only methods, such as levonorgestrel (Plan B) or ulipristal acetate (Ella), are more commonly used for emergency contraception.

**Why Each Wrong Option is Incorrect**
**Option A:** Levonorgestrel is a progestin used in emergency contraception, making it an incorrect choice.
**Option B:** Ulipristal acetate is a selective progesterone receptor modulator (SPRM) used in emergency contraception, so it is also incorrect.
**Option C:** Copper IUDs are a non-hormonal method of emergency contraception, which makes this option incorrect as it is not about a medication.

**Clinical Pearl / High-Yield Fact**
When counseling patients about emergency contraception, it's essential to consider their medical history, including any allergies, current medications, and potential interactions.

**Correct Answer: D. Estrogen. Estrogen is not typically used in emergency contraceptions.**