They have actually fit curves for SERT occupancy vs oral dose and vs blood concentration for each of the drugs tested. Am J Psychiatry. 2004 May;161(5):826-35. Serotonin transporter occupancy of five selective serotonin reuptake inhibitors at different doses: an [11C]DASB positron emission tomography study. Meyer JH1, Wilson AA, Sagrati S, Hussey D, Carella A, Potter WZ, Ginovart N, Spencer EP, Cheok A, Houle S. Abstract   The full paper is availabl