Oral contraceptives: mechanism of action, dosing, safety, and efficacy

The most widely used form of hormonal contraception is the combination oral contraceptive (OC). Combination OCs can be monophasic, providing the same dose of estrogen and progestin daily, or multiphasic, offering varying doses of hormones throughout a 21- or 28-day cycle. The objective of OCs is to suppress ovulation by manipulating events throughout the ovulatory cycle to prevent pregnancy. The progestin and estrogen components of OCs suppress the mid-cycle surge of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The overall effect is to decidualize the endometrial bed and suppress mitotic activity. Initial formulations of OCs in the 1960s attempted to mimic the natural cycle; however, providing high doses of estrogen rather than lower doses of combined estrogen and progestin resulted in greater risk of serious adverse events. Today, OCs provide far lower levels of estrogen and progestin. The availability of formulations with drospirenone, a unique progestin pharmacokinetically similar to progestin and similar in structure to spironolactone, should widen usage of OCs. Although OCs are still associated with increased risk in certain patients and are contraindicated in others, they remain effective but require diligent usage.