Document Type


Degree Name



Dept. of Public Health & Preventive Medicine.


Oregon Health & Science University


Background: Obesity alters pharmacokinetics (PK) of contraceptive hormones and has the potential to contribute to contraceptive failure. It is also a risk factor for venous thromboembolism (VTE). The current project aims to study the influence of the binding protein sex hormone binding globulin (SHBG) on levonorgestrel (LNG) pharmacokinetics, and to study changes in anticoagulation parameters protein C activity and free protein S, in a population of obese women initiating combined oral contraceptive pills (COCs). Methods: This project is a secondary analysis of data from a clinical trial conducted by Dr. Alison Edelman at Oregon Health & Science University. The original study evaluated three dosing regimens of COCs in a population of obese women. In this study, SHBG, protein C activity and protein S were measured at baseline at during use of COCs, and results were compared using mixed effects models. Results: SHBG rose differently depending on COC dose, altering the amount of pharmacologically active LNG. Body mass index was not related to SHBG or total LNG serum levels. Thrombotic biomarkers protein C and protein S did not demonstrate prothrombotic changes in obese women initiating COCs. Conclusions: The effect of SHBG on contraceptive pharmacokinetics remains incompletely understood, but SHBG’s strong binding of LNG has the potential to alter contraceptive effect in women of all BMIs. Protein C activity and Protein S remain unvalidated biomarkers and should not be used in assessing VTE risk for women initiating COCs.




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