Supra-physiological levels (COc uses hormone levels that are higher than the normal physiological levels in the body, which are typically lower in a natural cycle.)

"Pseudo-pregnancy" (causes changes in the body similar to those during pregnancy, tricking the body into thinking it’s pregnant, which prevents ovulation)

Suppression of the HPO (hypothalamic-pituitary-ovarian) axis

Pharmacokinetics are highly variable (The way the body absorbs, distributes, metabolizes, and eliminates the hormones in the COC can vary between individuals)

Individual serum levels vary (Each person's blood levels of the hormones may be different)

Suppression may not be absolute (Sometimes, the COC doesn’t fully prevent ovulation in every cycle, meaning ovulation could still occur)

Review: Contraception (Physiology 2)