On 19 March 1998, the Utrecht University Hospital (Academisch Ziekenhuis Utrecht) announced that in 1996 an international experiment with an anticoagulation drug had been halted after the death of seventeen patients. In the experiment, 1,316 patients participated, 665 of whom received aspirin to reduce the risk of a new stroke. The other 651 patients received the anticoagulation drug which aimed at preventing coagulation in the brain. Of the latter group, 53 patients had serious hemorrages and seventeen died. In the aspirin group six patients had similar complications and one died. The research team supposes that the anti-coagulation drug has diluted the blood too much, so it could leak away through damaged vascular walls. The experiment had been examined and approved by the medical ethical commissions of all 58 participating hospitals. After the first experiment was stopped, a new experiment with an adapted anti-coagulation drug was started, again after the approval of the 58 hospitals concerned. So far, only 135 patients – out of 4,500 needed – have agreed to participate.