What is the mechanism of action for emergency contraceptive pills?

• A. They induce menstruation.
• B. They prevent ovulation or fertilization.
• C. They act as a permanent contraceptive.
• D. They enhance sperm motility.

Answer: (B)

The mechanism of action for emergency contraceptive pills primarily involves preventing ovulation or fertilization. These pills contain hormones, such as levonorgestrel or ulipristal acetate, which work by delaying or inhibiting the release of an egg from the ovary. If the egg is not released, it cannot be fertilized by sperm, effectively preventing pregnancy.

Additionally, if ovulation has already occurred, emergency contraceptive pills may alter the movement of sperm through the reproductive tract, making it more difficult for the sperm to reach the egg, or they may change the lining of the uterus to create an environment less suitable for implantation. However, their primary function is to prevent ovulation.

Understanding this mechanism is crucial for effective use of emergency contraceptive pills, as they are most effective when taken shortly after unprotected intercourse, ideally within 72 hours, but can still be effective up to five days later.