The purpose of this study is to determine the effects of obesity on the pharmacokinetics of the levonorgestrel (LNG) only emergency contraceptive (EC) regimen and on markers of ovulation

Primary hypothesis:

1) Obese users of LNG-EC have a pharmacokinetic profile that is consistent with a larger volume of distribution of LNG.

Secondary hypothesis:

1. Alterations in these pharmacokinetic parameters of the LNG-EC regimen in obese women affect the primary mechanism of action, which is inhibition of ovulation.
2. Obesity may affect other factors that alter levels of LNG, such as sex-hormone binding globulin (SHBG) and albumin, which bind LNG and potentially lowers the amount of free LNG.

Inclusion Criteria:

• Women between ages 18-35 years

  • Regular menstrual cycles (24-35 days) for the past 2 months
  • Ovulatory at defined by midluteal progesterone level >3 ng/mL (Day 18-25)
  • Belongs to one of the following categories: normal weight (BMI = 18.5-24.9 kg/m2), obese (BMI = 30-39.9 kg/m2) or extremely obese (BMI ≥ 40 kg/m2)
  • Participant has no intention of or desire to conceive (e.g., active attempt to become pregnant or in vitro fertilization) for the duration of the study
  • Participant agrees to consistently use an effective method of nonhormonal contraception throughout the duration of study, which could include: condoms (male or female) with or without a spermicidal agent, diaphragm or cervical cap with spermicide, non-hormonal intra-uterine devise (IUD), or sterilization.
  • Able to give informed consent

Exclusion Criteria:

• • Known renal or liver disease

  • Known pituitary disorder
  • Known adrenal disorder
  • Known thyroid disorder
  • Use of medication known to alter the cytochrome P450 system
  • Use of depot-medroxyprogesterone acetate in the previous 6 months or any other hormonal contraceptive in the previous 3 months
  • Currently breastfeeding
  • Pregnant
  • Pregnancy in the prior month
  • Known allergy to medication
  • Other specific contraindications to LNG EC

Non-smoking women between ages 18-35 years with regular menstrual cycles (24-35 days) will be enrolled, to include 10 normal weight (BMI = 18.5-24.9 kg/m2) women, 10 obese (BMI = 30-39.9 kg/m2) and 10 extremely obese (BMI ≥ 40 kg/m2) women