Catha edulis Forsk leaves " Khat " are chewed daily by a high proportion of the adult population in Yemen .The present study investigated the relationship between blood coagulation and khat chewing .In our study , we investigated the blood coagulation tests in two groups namely khat chewers group (n:30) and non– khat chewers group (n:60). The blood coagulation tests included bleeding time , clotting time , prothrombin time , partial thromboplastin time and  platelets count. Statistical testing  for data analysis included the student's t-test and chi 2 test. The results presented show the level of  bleeding time , clotting time  ,  prothrombin time , platelets count  and platelets  aggregation   to be significantly different between khat chewers and non – khat chewers  (p< 0.05) , we observed decrease in bleeding time , clotting time and prothrombin time in khat chewers less than normal values and we also observed  enhance in platelets aggregation in khat chewers in comparison  with  non – khat chewers . The results presented show the level of partial thromboplastin time  to be non -significantly different (p > 0.05) between both groups . The study concluded the khat chewing effects on blood coagulation physiology and consider as risk factor for blood coagulation  system.

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