This study was a randomized, investigator-blinded, cross-over, clinic trial using twenty-four healthy women aged 18-35. All women received two months of the birth control patch or birth control pill, two months without any drug, then two months of the alternative drug. The birth control patch contained 0.75 milligrams ethinyl estradiol and 6 milligrams norelgestromin. The birth control pill contained 35 micrograms ethinyl estradiol and 250 micrograms norgestimate. Blood samples were taken before and after each treatment and were analyzed for the following lab values: D-dimer, von Willebrand factor, factor VIII, total and free protein S, antithrombin, fibrinogen, C-reactive protein and normalized activated protein C sensitivity ratio (nAPCsr). Two thrombin generation-based assays were used: the α2macroglobulin-thrombin endpoint method (α2M-IIa) and calibrated automated thrombinography (CAT).