Prior studies examining the pharmacokinetics, safety, and efficacy of the new etonogestrel-containing single rod implantable contraceptive device, Implanon, did not include women who exceeded 130% of ideal body weight. Yet, as these women comprise a significant portion of the U.S. population, studies of Implanon in obese women are essential. The proposed study represents an important first step in addressing the lack of data on Implanon in obese women. We aim to examine the pharmacokinetics of Implanon in obese women during the first 6 months of use and to provide data on the acceptability, side effect profile, and ease of insertion, palpation, and removal in these women. We also aim to collect samples for future validation studies of the use of the blood spot (finger-stick blood sample on filter paper) as a method of determining plasma etonogestrel.

Inclusion Criteria:

• premenopausal with a uterus and at least one ovary
• willing and able to sign the informed consent
• willing to comply with the study protocol and visit schedule
• have a body mass index of less than 25, or greater than or equal to 30
• weight stable

Exclusion Criteria:

• known or suspected pregnancy
• delivery (vaginal or cesarean) within 4 months of device insertion
• abortion (first or second trimester) within 4 months of device insertion
• contraindications to Implanon use
• hemophilia
• undiagnosed abnormal genital bleeding
• hypersensitivity or allergy to any components of Implanon
• personal or family history of thrombosis or thromboembolic disorders
• hepatic tumors or active liver disease
• known or suspected carcinoma of the breast or history of breast cancer
• more that one cardiovascular risk factor such as hypertension or diabetes
• known history of PCOS, diabetes, or glucose abnormality
• present use or use within 2 months of device insertion of a CYP3A4 inducer
• breastfeeding women
• use of an investigational drug within 2 months of device insertion
• use of injectable contraception within 6 months of device insertion
• planning a pregnancy in the next 12 months
• known HIV infection
• smoking over the age of 35

Participants will be recruited from resident and faculty practices at the University of Chicago outpatient facilities and from the University of Chicago clinical trails database of past study participants.