The degree of suppression and subsequent activation of the hypothalamic-pituitary-ovarian axis during the hormone-free interval in combined oral contraceptive (COC) hormone users varies depending on the dose of ethinyl estradiol in the formulation. This variation in activation may be associated with different side effects during the hormone free interval. Progesterone (P) remained suppressed during all 6 COC regimens (<1.8 ng/mL), which indicates continuous contraceptive efficacy during the 7-day hormone free interval of all formulations studied.

Inclusion Criteria:

• Healthy, reproductive age women
• 18 to 35 years old,
• seeking contraception from the general gynecology clinics of the LAC and USC Medical Center w
• taking one of 6 possible monophasic COC formulations for at least 3 cycles prior to enrollment
• regular menstrual cycles prior to COCs

Exclusion Criteria:

• Irregular bleeding
• bilateral oophorectomy
• amenorrhea
• hormone-sensitive cancer
• concurrent medications known to interfere with steroid metabolism (i.e., barbiturates, phenytoin, carbamazepine, ethosuximide, primidone, rifampin, tetracycline)

Healthy, reproductive age women 18 to 35 years old, who were seeking contraception from the general gynecology clinics of the LAC and USC Medical Center were recruited. The research team identified potential candidates who were taking one of 6 possible monophasic COC formulations. Informed consent was obtained from participants by the research staff. To be eligible for participation, women reported regular menstrual cycles prior to COCs, and had taken at least 3 cycles of the same monophasic COC prior to enrollment.