Abbreviation for “1-desamino-8-d-arginine vasopressin.” DDAVP is a synthetic version of antidiuretic hormone (ADH) originally developed to treat diabetes insipidus. This medication also has a useful side effect applicable to transfusion medicine: It causes release of von Willebrand factor and coagulation factor VIII (FVIII) from endothelial cells, and may also directly increase adhesion proteins on the endothelial cells. DDAVP is approved for temporary use in certain forms of von Willebrand Disease and Hemophilia A because of the effect on vWF and FVIII. It is also useful in temporary reversal of platelet dysfunction caused by chronic renal failure, due to the vWF increase and maybe the effect on adhesion proteins. DDAVP cannot be given over and over, however, as the response dims with use more than once every 24 hours or so (probably due to depletion of vWF stores in the endothelial cells). This diminished effect is called “tachyphylaxis.”