The purpose of this study is to administer a combined oral contraceptive containing ethinyl estradiol and norgestimate with the HIV treatment of efavirenz to healthy females in order to assess if the concentrations of the oral contraceptives change. The safety of this treatment regimen will also be studied.

Inclusion Criteria:

• Women of childbearing potential with intact ovarian function who have been on a stable method of oral contraceptives for at least 2 months prior to the start of the study.
• Documented acceptable Pap smear within 1 year of the start of the study
• BMI of 18-32 kg/m²

Exclusion Criteria:

• Males
• Subjects with abnormal menstrual cycle within 2 months prior to the start of the study
• History of conditions in which oral contraceptives are contraindicated
• History of migraine with focal aura
• History of uncontrolled hypertension
• Positive screening test for HIV-1,-2, HIV viral RNA, Hepatitis B surface antigen, or Hepatitis C antibody
• History of diagnosed mental illness or suicidal ideation