## **Core Concept**
The "morning after pill" refers to emergency contraception used to prevent pregnancy after unprotected sex or contraceptive failure. It primarily works by inhibiting or delaying ovulation. The most commonly used emergency contraceptive pills contain synthetic hormones.

## **Why the Correct Answer is Right**
The correct answer, , contains **levonorgestrel**, a synthetic progestogen. Levonorgestrel works by inhibiting or delaying ovulation, thereby preventing fertilization of the egg by sperm. It can also affect the endometrium, making it less likely for a fertilized egg to implant. Levonorgestrel is specifically used for emergency contraception and is effective when taken within 72 hours of unprotected sex.

## **Why Each Wrong Option is Incorrect**
- **Option A:** is incorrect because, while mifepristone (RU486) is an antiprogestin used for medical abortion, it is not the primary component of the morning after pill.
- **Option B:** is incorrect because estrogen and progesterone are natural hormones, not typically used in emergency contraceptive pills due to their side effects and the availability of more effective synthetic alternatives.
- **Option D:** is incorrect because, although ulipristal acetate is another medication used for emergency contraception, it is not as commonly referenced as levonorgestrel for the "morning after pill."

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the effectiveness of emergency contraception, including the morning after pill, decreases over time. It is most effective when taken as soon as possible after unprotected sex, ideally within 24 hours, but it can be used up to 72 hours later.

## **Correct Answer:** . Levonorgestrel