Increased fibrinolytic activity during use of oral contraceptives is counteracted by an enhanced factor XI-independent down regulation of fibrinolysis. A randomized cross-over study of two low-dose oral contraceptives - Meijers, JCM; Middeldorp, S; Tekelenberg, W; van den Ende, AE; Tans, G; Prins, MH; Rosing, J; Buller, HR; Bouma, BN (Thromb Haemost, 2000)