**Core Concept**
The post coital pill, also known as emergency contraception, is a medication used to prevent pregnancy after unprotected sex or contraceptive failure. It works by delaying ovulation, interfering with fertilization, or preventing implantation of a fertilized egg.

**Why the Correct Answer is Right**
The post coital pill typically contains hormones such as levonorgestrel, which is a synthetic progestin. When taken within 72 hours of unprotected sex, levonorgestrel works by preventing or delaying ovulation, thereby reducing the likelihood of fertilization. It may also interfere with the implantation of a fertilized egg in the uterus. The exact mechanism is not fully understood, but it is thought to involve the inhibition of luteinizing hormone (LH) release, which is necessary for ovulation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the active ingredient in the post coital pill. While there are other forms of emergency contraception available, such as ulipristal acetate, the most commonly used medication is levonorgestrel.

**Option B:** This option is incorrect because it is not a known ingredient in the post coital pill.

**Option C:** This option is incorrect because it is not a hormone and is not used as an emergency contraceptive.

**Clinical Pearl / High-Yield Fact**
The post coital pill is most effective when taken within 24 hours of unprotected sex, with a 75% efficacy rate. Efficacy decreases to 61% when taken between 25-48 hours, and to 42% when taken between 49-72 hours.

**Correct Answer: C.