A 22-year-old woman comes to the physician to discuss the prescription of an oral contraceptive. She has no history of major medical illness and takes no medications. She does not smoke cigarettes. She is sexually active with her boyfriend and has been using condoms for contraception. Physical examination shows no abnormalities. She is prescribed combined levonorgestrel and ethinylestradiol tablets. Which of the following is the most important mechanism of action of this drug in the prevention of pregnancy?

Question

Quizplus · Accepted Answer

Eductional Objective: The most important mechanism of action of combined oral contraceptives in preventing ovulation is the inhibition of the LH surge. The estrogen and progestin in combined OCPs provide negative feedback to the hypothalamus, preventing the release of GnRH and, subsequently, both FSH and LH. This decreased gonadotropin secretion prevents the spike in estrogen (released from the Graafian follicle) necessary to induce the LH surge in the pituitary, which then initiates ovulation. This significantly reduces the possibility of successful fertilization (< 1% with perfect use; 9% with typical use).

A 22-Year-Old Woman Comes to the Physician to Discuss the Prescription